< Назад | Содержимое | Далее >

‌ACCESSORIES & EQUIPMENT

Data Communications - Diagnostic Information and Procedures - Volt

DIAGNOSTIC INFORMATION AND PROCEDURES

DTC U1817: LOST COMMUNICATION WITH HYBRID POWERTRAIN CONTROL MODULE ON POWERTRAIN EXPANSION CAN BUS

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach.

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC U1817

Lost Communication with Hybrid Powertrain Control Module on Powertrain Expansion CAN Bus For symptom byte information, refer to Symptom Byte List .

Diagnostic Fault Information

Circuit/System Description

Devices connected to the powertrain high speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the devices. The devices have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver device as an availability indication of the transmitter device. Each message contains the identification number of the transmitter device.

The Motor Control Modules and the Hybrid Powertrain Control Module 1 are all internal to the Power Inverter

Module. All circuits to the Hybrid Powertrain Control Module 1 are also internal to the Power Inverter Module and replaced as a single component.

Communication diagnostics for the serial data, including device power and ground as well as the wakeup circuits for Motor Control Modules and the Hybrid Powertrain Control Module 1 are all diagnosed from external sources only to the Power Inverter Module connector because any circuit fault condition within the Power Inverter Module will cause a complete replacement.

Conditions for Running the DTC

The system voltage is more than 10 V.

The vehicle power mode master requires serial data communication to occur from this specific device.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter device availability has not been received.

Action Taken When the DTC Sets DTC U1817 is a type A DTC. Conditions for Clearing the DTC DTC U1817 is a type A DTC. Diagnostic Aids

Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves

automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

A device on the data communication circuit was disconnected while the communication circuit is awake.

Power to one or more devices was interrupted during diagnosis.

A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold.

Battery power was restored to the vehicle and devices on the communication circuit did not all re- initialize at the same time.

If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

A device may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U-code.

Do not replace a device reporting a U-code. The U-code identifies which device needs to be diagnosed for a communication issue.

Communication may be available between the device and the scan tool with one or more GMLAN serial data systems inoperative. This condition is due to the device using multiple GMLAN busses.

Use Data Link References to determine what GMLAN serial data communications the non communicating device uses.

The device may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the non communicating device.

Reference Information

Schematic Reference

Data Communication Schematics Control Module References

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Vehicle in Service Mode.

2. Verify that DTC U0293 is not set.

If DTC U0293 is set

Refer to DTC U0100-U02FF .

If DTC U0293 is not set

3. Verify that DTC U0073, U0074, U0077, U0078, U007A, P06E4, P1EB9, U1814, U2099, B1325, B1330, B1370, B1380, B1424, B1428, B1440, B1441, B1517, C0800, C0899, C12E1, P0560, or P0562 is not

set.

If any of the DTCs are set

Refer to Diagnostic Trouble Code (DTC) List - Vehicle .

If none of the DTCs are set

4. Verify that DTCs U1818, U1821, and U182D are not set.

If all of the DTCs are set together

Refer to DTC U0074 .

If all of the DTCs are not set together

5. Refer to Circuit/System Testing.

Circuit/System Testing

NOTE: Use the schematics and connector end views to identify the device's ground, B+, ignition, accessory wake up serial data 2, and serial data circuit terminals.

1. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the X1 and X2 harness connectors at the T6 Power Inverter Module. It may take up to 2 minutes for all vehicle systems to power down.

2. Test for less than 10 Ω between the T6 Power Inverter Module case and ground.

If 10 Ω or greater

Check the ground connection and ground strap for the open/high resistance.

If less than 10 Ω

3. Vehicle in Service Mode.

4. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the B+ circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the B+ circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the T6 Power Inverter Module.

If the test lamp illuminates

5. Vehicle in Service Mode.

6. If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the ignition circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is OK and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the ignition circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the T6 Power Inverter Module.

If the test lamp illuminates

7. Vehicle in Service Mode.

8. If equipped, verify a test lamp illuminates between the accessory wakeup serial data 2 circuit terminal and ground.

If the test lamp does not illuminate

1. Vehicle OFF, disconnect the harness connectors at the K114B Hybrid/EV Powertrain Control Module 2.

2. Test for infinite resistance between the accessory wakeup serial data 2 circuit and ground. If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance

3. Test for less than 2 Ω in the accessory wakeup serial data 2 circuit end to end. If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, replace the K114B Hybrid/EV Powertrain Control Module 2.

If the test lamp illuminates

9. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the harness connectors at the device setting the DTC. It may take up to 2 minutes for all vehicle systems to power down.

10. Test for less than 2 Ω in each of the powertrain high speed GMLAN serial data circuits end to end between the T6 Power Inverter Module and the device setting the DTC.

If 2 Ω or greater

Repair the open/high resistance in the serial data circuit.

If less than 2 Ω

11. Replace the T6 Power Inverter Module.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Serial Data Circuit Wiring Repairs

Control Module References for device replacement, programming and setup

DTC U1818: LOST COMMUNICATION WITH ENGINE CONTROL MODULE ON POWERTRAIN EXPANSION COMMUNICATION BUS

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

Review Strategy Based Diagnosis for an overview of the diagnostic approach.

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC U1818

Lost Communication with Engine Control Module on Powertrain Expansion Communication Bus For symptom byte information, refer to Symptom Byte List .

Diagnostic Fault Information

Circuit/System Description

Devices connected to the serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the devices. The devices have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver device as an availability indication of the transmitter device. Each message contains the identification number of the transmitter device.

Conditions for Running the DTC

The system voltage is at least 10 V.

The vehicle power mode master requires serial data communication to occur from this specific device.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter device availability has not been received.

Action Taken When the DTC Sets DTC U1818 is a type A DTC. Conditions for Clearing the DTC DTC U1818 is a type A DTC.

Diagnostic Aids

Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves

automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

A device on the data communication circuit was disconnected while the communication circuit is awake.

Power to one or more devices was interrupted during diagnosis.

A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold.

Battery power was restored to the vehicle and devices on the communication circuit did not all re- initialize at the same time.

If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

A device may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U-code.

Do not replace a device reporting a U-code. The U-code identifies which device needs to be diagnosed for a communication issue.

Communication may be available between the device and the scan tool with one or more GMLAN serial data systems inoperative. This condition is due to the device using multiple GMLAN busses.

Use Data Link References to determine what GMLAN serial data communications the non communicating device uses.

The device may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the non communicating device.

Reference Information

Schematic Reference

Data Communication Schematics Control Module References

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Vehicle in Service Mode.

2. Verify that DTC U0100 is not set.

If DTC U0100 is set

Refer to DTC U0100-U02FF .

If DTC U0100 is not set

3. Verify that DTC U0073, U0074, U0077, U0078, U007A, P06E4, P1EB9, U1814, U2099, B1325, B1330, B1370, B1380, B1424, B1428, B1440, B1441, B1517, C0800, C0899, C12E1, P0560, or P0562 is not

set.

If any of the DTCs are set

Refer to Diagnostic Trouble Code (DTC) List - Vehicle .

If none of the DTCs are set

4. Verify that DTCs U1817, U1821, and U182D are not set.

If all of the DTCs are set together

Refer to DTC U0074 .

If all of the DTCs are not set together

5. Refer to Circuit/System Testing.

Circuit/System Testing

NOTE: Use the schematics and connector end views to identify the device's ground, B+, ignition, accessory wake up serial data 2, and serial data circuit terminals.

1. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the harness connectors at the K20 Engine Control Module. It may take up to 2 minutes for all vehicle systems to power down.

2. Test for less than 10 Ω between each ground circuit terminal and ground.

If 10 Ω or greater

1. Vehicle OFF.

2. Test for less than 2 Ω in the ground circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, repair the open/high resistance in the ground connection.

If less than 10 Ω

3. Vehicle in Service Mode.

4. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the B+ circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the B+ circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K20 Engine Control Module.

If the test lamp illuminates

5. Vehicle in Service Mode.

6. If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the ignition circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is OK and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the ignition circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K20 Engine Control Module.

If the test lamp illuminates

7. Vehicle in Service Mode.

8. If equipped, verify a test lamp illuminates between the accessory wakeup serial data 2 circuit terminal and ground.

If the test lamp does not illuminate

1. Vehicle OFF, disconnect the harness connectors at the K114B Hybrid/EV Powertrain Control Module 2.

2. Test for infinite resistance between the accessory wakeup serial data 2 circuit and ground. If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance

3. Test for less than 2 Ω in the accessory wakeup serial data 2 circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, replace the K114B Hybrid/EV Powertrain Control Module 2.

If the test lamp illuminates

9. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the harness connectors at the device setting the DTC. It may take up to 2 minutes for all vehicle systems to power down.

10. Test for less than 2 Ω in each of the powertrain high speed GMLAN serial data circuits end to end between the K20 Engine Control Module and the device setting the DTC.

If 2 Ω or greater

Repair the open/high resistance in the serial data circuit.

If less than 2 Ω

11. Replace the K20 Engine Control Module.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Serial Data Circuit Wiring Repairs

Control Module References for device replacement, programming and setup

DTC U182D: LOST COMMUNICATION WITH HYBRID POWERTRAIN CONTROL MODULE 2 ON POWERTRAIN EXPANSION COMMUNICATION BUS

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach.

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC U182D

Lost Communication with Hybrid Powertrain Control Module 2 on Powertrain Expansion Communication Bus

For symptom byte information, refer to Symptom Byte List .

Diagnostic Fault Information

Circuit/System Description

The serial data circuit is the means by which the devices in the vehicle communicate with each other. Once the scan tool is connected to the serial data circuit through the data link connector (DLC), the scan tool can be used to monitor each device for diagnostic purposes and to check for diagnostic trouble codes (DTC). When the vehicle is on, each device communicating on the serial data circuit sends a state of health message to ensure that the device is operating properly. When a device stops communicating on the serial data circuit, for example if the device loses power or ground, the state of health message it normally sends on the serial data circuit disappears. Other devices on the serial data circuit, which expect to receive that state of health message, detect its absence; those devices in turn set a DTC associated with the loss of state of health of the non communicating device. A loss of serial data communications DTC does not represent a failure of the devices that contain the stored DTC.

Conditions for Running the DTC The system voltage is at least 11 V. Conditions for Setting the DTC

A supervised periodic message that includes the transmitter device availability has not been received for 10 seconds.

Action Taken When the DTC Sets The DTC U182D is a type B DTC. Conditions for Clearing the DTC The DTC U182D is a type B DTC. Diagnostic Aids

Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves

automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

A device on the data communication circuit was disconnected while the communication circuit is awake.

Power to one or more devices was interrupted during diagnosis.

A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold.

Battery power was restored to the vehicle and devices on the communication circuit did not all re- initialize at the same time.

If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

A device may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U-code.

Do not replace a device reporting a U-code. The U-code identifies which device needs to be diagnosed for a communication issue.

Communication may be available between the device and the scan tool with one or more GMLAN serial data systems inoperative. This condition is due to the device using multiple GMLAN busses.

Use Data Link References to determine what GMLAN serial data communications the non communicating device uses.

The device may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the non communicating device.

Reference Information

Schematic Reference

Data Communication Schematics Control Module References

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Vehicle in Service Mode.

2. Verify that DTC U0073, U0074, U0077, U0078, U007A, P06E4, P1EB9, U1814, U2099, B1325, B1330, B1370, B1380, B1424, B1428, B1440, B1441, B1517, C0800, C0899, C12E1, P0560, or P0562 is not

set.

If any of the DTCs are set

Refer to Diagnostic Trouble Code (DTC) List - Vehicle .

If none of the DTCs are set

3. Verify that DTCs U1817, U1818, and U1821 are not set.

If all of the DTCs are set together

Refer to DTC U0074 .

If all of the DTCs are not set together

4. Refer to Circuit/System Testing.

Circuit/System Testing

NOTE: Use the schematics and connector end views to identify the device's ground, B+, ignition, accessory wake up serial data, and serial data circuit terminals.

1. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the harness connectors at the K114B Hybrid/EV Powertrain Control Module 2. It may take up to 2 minutes for all vehicle systems to power down.

2. Test for less than 10 Ω between each ground circuit terminal and ground.

If 10 Ω or greater

1. Vehicle OFF.

2. Test for less than 2 Ω in the ground circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, repair the open/high resistance in the ground connection.

If less than 10 Ω

3. Vehicle in Service Mode.

4. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the B+ circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the B+ circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance, replace the K114B Hybrid/EV Powertrain Control Module 2.

If the test lamp illuminates

5. Vehicle in Service Mode.

6. If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the ignition circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is OK and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the ignition circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance, replace the K114B Hybrid/EV Powertrain Control Module 2.

If the test lamp illuminates

7. Vehicle in Service Mode.

8. If equipped, verify a test lamp illuminates between the accessory wakeup serial data circuit terminal and ground.

If the test lamp does not illuminate

1. Vehicle OFF, disconnect the harness connectors at the K9 Body Control Module.

2. Test for infinite resistance between the accessory wakeup serial data circuit and ground. If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance

3. Test for less than 2 Ω in the accessory wakeup serial data circuit end to end. If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, replace the K9 Body Control Module.

If the test lamp illuminates

9. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the harness connectors at the device setting the DTC. It may take up to 2 minutes for all vehicle systems to power down.

10. Test for less than 2 Ω in each powertrain high speed GMLAN serial data circuits end to end between the K114B Hybrid/EV Powertrain Control Module 2 and the device setting the DTC.

If 2 Ω or greater

Repair the open/high resistance in the serial data circuit.

If less than 2 Ω

11. Replace the K114B Hybrid/EV Powertrain Control Module 2.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Serial Data Circuit Wiring Repairs

Control Module References for device replacement, programming and setup

DTC U182E OR U182F: DRIVE MOTOR CONTROL MODULE LOST COMMUNICATION WITH HYBRID PCM 2 ON POWERTRAIN EXPANSION COMMUNICATION BUS

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach.

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC U182E

Drive Motor Control Module 1 Lost Communication with Hybrid Powertrain Control Module 2 on Powertrain Expansion Communication Bus

DTC U182F

Drive Motor Control Module 2 Lost Communication with Hybrid Powertrain Control Module 2 on Powertrain Expansion Communication Bus

For symptom byte information, refer to Symptom Byte List .

Diagnostic Fault Information

Circuit/System Description

The serial data circuit is the means by which the devices in the vehicle communicate with each other. Once the scan tool is connected to the serial data circuit through the data link connector (DLC), the scan tool can be used

to monitor each device for diagnostic purposes and to check for diagnostic trouble codes (DTC). When the vehicle is on, each device communicating on the serial data circuit sends a state of health message to ensure that the device is operating properly. When a device stops communicating on the serial data circuit, for example if the device loses power or ground, the state of health message it normally sends on the serial data circuit disappears. Other devices on the serial data circuit, which expect to receive that state of health message, detect its absence; those devices in turn set a DTC associated with the loss of state of health of the non communicating device. A loss of serial data communications DTC does not represent a failure of the devices that contain the stored DTC.

Conditions for Running the DTC The system voltage is at least 10 V. Conditions for Setting the DTC

A supervised periodic message that includes the transmitter device availability has not been received.

Action Taken When the DTC Sets

The DTCs U182E and U182F are type B DTCs.

Conditions for Clearing the DTC

The DTCs U182E and U182F are type B DTCs.

Diagnostic Aids

Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves

automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

A device on the data communication circuit was disconnected while the communication circuit is awake.

Power to one or more devices was interrupted during diagnosis.

A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold.

Battery power was restored to the vehicle and devices on the communication circuit did not all re- initialize at the same time.

If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

A device may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U-code.

Do not replace a device reporting a U-code. The U-code identifies which device needs to be diagnosed for a communication issue.

Communication may be available between the device and the scan tool with one or more GMLAN serial data systems inoperative. This condition is due to the device using multiple GMLAN busses.

Use Data Link References to determine what GMLAN serial data communications the non communicating device uses.

The device may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the non communicating device.

Reference Information

Schematic Reference

Data Communication Schematics Control Module References

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Vehicle in Service Mode.

2. Verify that DTC U0073, U0074, U0077, U0078, U007A, U1814, U2099, B1325, B1330, B1370, B1380, B1424, B1428, B1440, B1441, B1517, C0800, C0899, C12E1, P0560, or P0562 is not set.

If any of the DTCs are set

Refer to Diagnostic Trouble Code (DTC) List - Vehicle .

If none of the DTCs are set

3. Refer to Circuit/System Testing.

Circuit/System Testing

NOTE: Use the schematics and connector end views to identify the device's ground,

B+, ignition, accessory wake up serial data, and serial data circuit terminals.

1. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the harness connectors at the K114B Hybrid/EV Powertrain Control Module 2. It may take up to 2 minutes for all vehicle systems to power down.

2. Test for less than 10 Ω between each ground circuit terminal and ground.

If 10 Ω or greater

1. Vehicle OFF.

2. Test for less than 2 Ω in the ground circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, repair the open/high resistance in the ground connection.

If less than 10 Ω

3. Vehicle in Service Mode.

4. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the B+ circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the B+ circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance, replace the K114B Hybrid/EV Powertrain Control Module 2.

If the test lamp illuminates

5. Vehicle in Service Mode.

6. If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the ignition circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is OK and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the ignition circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance, replace the K114B Hybrid/EV Powertrain Control Module 2.

If the test lamp illuminates

7. Vehicle in Service Mode.

8. If equipped, verify a test lamp illuminates between the accessory wakeup serial data circuit terminal and ground.

If the test lamp does not illuminate

1. Vehicle OFF, disconnect the harness connectors at the K9 Body Control Module.

2. Test for infinite resistance between the accessory wakeup serial data circuit and ground. If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance

3. Test for less than 2 Ω in the accessory wakeup serial data circuit end to end. If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, replace the K9 Body Control Module.

If the test lamp illuminates

9. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the X1 harness connector at the T6 Power Inverter Module. It may take up to 2 minutes for all vehicle systems to power down.

10. Test for less than 2 Ω in each powertrain high speed GMLAN serial data circuits end to end between the K114B Hybrid/EV Powertrain Control Module 2 and the T6 Power Inverter Module.

If 2 Ω or greater

Repair the open/high resistance in the serial data circuit.

If less than 2 Ω

11. Replace the K114B Hybrid/EV Powertrain Control Module 2.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Serial Data Circuit Wiring Repairs

Control Module References for device replacement, programming and setup

DTC U1833: LOST COMMUNICATION WITH ELECTRONIC BRAKE CONTROL MODULE ON CHASSIS EXPANSION CAN BUS

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach.

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC U1833

Lost Communication with Electronic Brake Control Module on Chassis Expansion CAN Bus For symptom byte information, refer to Symptom Byte List .

Diagnostic Fault Information

Circuit/System Description

Devices connected to the serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the devices. The devices have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver device as an availability indication of the transmitter device. Each message contains the identification number of the transmitter device.

Conditions for Running the DTC The system voltage is at least 10 V. Conditions for Setting the DTC

A supervised periodic message that includes the transmitter device availability has not been received.

Action Taken When the DTC Sets

A driver information center message and/or a warning indicator may be displayed. The DTC U1833 is a type B DTC.

Conditions for Clearing the DTC The DTC U1833 is a type B DTC. Diagnostic Aids

Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U code present. However, there is no associated "current" or "active" status. Loss of communication U codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

A device on the data communication circuit was disconnected while the communication circuit is awake.

Power to one or more devices was interrupted during diagnosis.

A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold.

Battery power was restored to the vehicle and devices on the communication circuit did not all re- initialize at the same time.

If a loss of communication U code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

A device may have a U code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U code.

Do not replace a device reporting a U code. The U code identifies which device needs to be diagnosed for a communication issue.

Communication may be available between the device and the scan tool with one or more GMLAN serial data systems inoperative. This condition is due to the device using multiple GMLAN busses.

Use Data Link References to determine what GMLAN serial data communications the non communicating device uses.

The device may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the non communicating device.

Reference Information

Schematic Reference

Data Communication Schematics Control Module References

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Vehicle in Service Mode.

2. Verify that DTC U0121 or U0129 is not set.

If any of the DTCs are set

Refer to DTC U0100-U02FF .

If none of the DTCs are set

3. Verify that DTC U0073, U0074, U0077, U0078, U007A, P06E4, P1EB9, U1814, U2099, B1325, B1330, B1370, B1380, B1424, B1428, B1440, B1441, B1517, C0800, C0899, C12E1, P0560, or P0562 is not

set.

If any of the DTCs are set

Refer to Diagnostic Trouble Code (DTC) List - Vehicle .

If none of the DTCs are set

4. Refer to Circuit/System Testing.

Circuit/System Testing

NOTE: Use the schematics and connector end views to identify the device's ground, B+, ignition, accessory wake up serial data 2, and serial data circuit terminals.

1. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. Disconnect the harness connectors at the K17 Electronic Brake Control Module. It may take up to 2 min for all vehicle systems to power down.

2. Test for less than 10 Ω between each ground circuit terminal and ground.

If 10 Ω or greater

1. Vehicle OFF.

2. Test for less than 2 Ω in the ground circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, repair the open/high resistance in the ground connection.

If less than 10 Ω

3. Vehicle in Service Mode.

4. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the B+ circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the B+ circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K17 Electronic Brake Control Module.

If the test lamp illuminates

5. Vehicle in Service Mode.

6. If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the ignition circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is OK and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the ignition circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K17 Electronic Brake Control Module.

If the test lamp illuminates

7. Vehicle in Service Mode.

8. If equipped, verify a test lamp illuminates between the accessory wakeup serial data 2 circuit terminal and ground.

If the test lamp does not illuminate

1. Vehicle OFF, disconnect the harness connectors at the K114B Hybrid/EV Powertrain Control Module 2.

2. Test for infinite resistance between the accessory wakeup serial data 2 circuit and ground. If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance

3. Test for less than 2 Ω in the accessory wakeup serial data 2 circuit end to end. If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, replace the K114B Hybrid/EV Powertrain Control Module 2.

If the test lamp illuminates

9. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. Disconnect the harness connectors at the device setting the DTC. It may take up to 2 min for all vehicle systems to power down.

10. Test for less than 2 Ω in each Chassis high speed GMLAN serial data circuits end to end between the K17 Electronic Brake Control Module and the device setting the DTC.

If 2 Ω or greater

Repair the open/high resistance in the serial data circuit.

If less than 2 Ω

11. Replace the K17 Electronic Brake Control Module.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Serial Data Circuit Wiring Repairs

Control Module References for device replacement, programming and setup

DTC U183E: LOST COMMUNICATION WITH TELEMATICS COMMUNICATION INTERFACE CONTROL MODULE ON LOW SPEED CAN BUS

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach.

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC U183E

Lost Communication with Telematics Communication Interface Control Module on Low Speed CAN Bus For symptom byte information, refer to Symptom Byte List .

Diagnostic Fault Information

Circuit/System Description

The serial data circuit is the means by which the devices in the vehicle communicate with each other. Once the scan tool is connected to the serial data circuit through the Data Link Connector (DLC), the scan tool can be

used to monitor each device for diagnostic purposes and to check for diagnostic trouble codes (DTCs). When the vehicle is ON, each device communicating on the serial data circuit sends a state of health message to ensure that the device is operating properly. When a device stops communicating on the serial data circuit, for example if the device loses power or ground, the state of health message it normally sends on the serial data circuit disappears. Other devices on the serial data circuit, which expect to receive that state of health message, detect its absence; those devices in turn set a DTC associated with the loss of state of health of the non communicating device. A loss of serial data communications DTC does not represent a failure of the devices that contain the stored DTC.

Conditions for Running the DTC

The system voltage is between 9 - 16 V.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter device availability has not been received.

Action Taken When the DTC Sets

The device is never signaled. Therefore, the specific subsystems will not function.

Conditions for Clearing the DTC

A current DTC clears when the malfunction is no longer present.

A history DTC clears when the device ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

Diagnostic Aids

Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U code present. However, there is no associated "current" or "active" status. Loss of communication U codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

A device on the data communication circuit was disconnected while the communication circuit is awake.

Power to one or more devices was interrupted during diagnosis.

A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold.

Battery power was restored to the vehicle and devices on the communication circuit did not all re- initialize at the same time.

If a loss of communication U code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

A device may have a U code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U code.

Do not replace a device reporting a U code. The U code identifies which device needs to be diagnosed for a communication issue.

Communication may be available between the device and the scan tool with one or more GMLAN serial data systems inoperative. This condition is due to the device using multiple GMLAN busses.

Use Data Link References to determine what GMLAN serial data communications the non communicating device uses.

The device may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the non communicating device.

Reference Information

Schematic Reference

Data Communication Schematics Control Module References

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Vehicle in Service Mode.

2. Verify that DTC U0198 is not set.

If DTC U0198 is set

Refer to DTC U0100-U02FF .

If DTC U0198 is not set

3. Verify that DTC U0073, U0074, U0077, U0078, U007A, P06E4, P1EB9, U1814, U2099, B1325, B1330, B1370, B1380, B1424, B1428, B1440, B1441, B1517, C0800, C0899, C12E1, P0560, or P0562 is not

set.

If any of the DTCs are set

Refer to Diagnostic Trouble Code (DTC) List - Vehicle .

If none of the DTCs are set

4. Refer to Circuit/System Testing.

Circuit/System Testing

NOTE: Use the schematics and connector end views to identify the device's ground, B+, ignition, serial data communication enable, and serial data circuit terminals.

1. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. Disconnect the harness connectors at the K73 Telematics Communication Interface Control Module. It may take up to 2 min for all vehicle systems to power down.

2. Test for less than 10 Ω between each ground circuit terminal and ground.

If 10 Ω or greater

1. Vehicle OFF.

2. Test for less than 2 Ω in the ground circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, repair the open/high resistance in the ground connection.

If less than 10 Ω

3. Vehicle in Service Mode.

4. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the B+ circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the B+ circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance, replace the K73 Telematics Communication Interface Control Module.

If the test lamp illuminates

5. Vehicle in Service Mode.

6. If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the ignition circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is OK and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the ignition circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance, replace the K73 Telematics Communication Interface Control Module.

If the test lamp illuminates

7. Vehicle in Service Mode.

8. If equipped, verify a test lamp illuminates between the serial data communication enable circuit terminal and ground.

If the test lamp does not illuminate

1. Vehicle OFF, disconnect the harness connectors at the K9 Body Control Module.

2. Test for infinite resistance between the serial data communication enable circuit and ground. If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance

3. Test for less than 2 Ω in the serial data communication enable circuit end to end. If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, replace the K9 Body Control Module.

If the test lamp illuminates

9. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. Disconnect the harness connectors at the device setting the DTC. It may take up to 2 min for all vehicle systems to power down.

10. Test for less than 2 Ω in the low speed GMLAN serial data circuits end to end between the K73 Telematics Communication Interface Control Module and the device setting the DTC.

If 2 Ω or greater

Repair the open/high resistance in the serial data circuit.

If less than 2 Ω

11. Replace the K73 Telematics Communication Interface Control Module.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Serial Data Circuit Wiring Repairs

Control Module References for device replacement, programming and setup

DTC U1845 OR U1846: DRIVE MOTOR CONTROL MODULE LOST COMMUNICATION WITH HYBRID POWERTRAIN CONTROL MODULE

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

Review Strategy Based Diagnosis for an overview of the diagnostic approach.

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC U1845

Drive Motor Control Module 1 Lost Communication with Hybrid Powertrain Control Module

DTC U1846

Drive Motor Control Module 2 Lost Communication with Hybrid Powertrain Control Module For symptom byte information, refer to Symptom Byte List .

Circuit/System Description

The Motor Control Modules and the Hybrid Powertrain Control Module 1 are all internal to the Power Inverter Module. The Motor Control Modules communicate only with the Hybrid Powertrain Control Module 1 with the Hybrid Powertrain Control Module 1 sending out diagnostic trouble code information to other devices regarding the Motor Control Modules. All circuits to the Hybrid Powertrain Control Module 1 and Motor Control Modules are also internal to the Power Inverter Module and replaced as a single component.

Communication diagnostics for the serial data, including device power and ground as well as the wakeup circuits for Motor Control Modules and the Hybrid Powertrain Control Module 1 are all diagnosed from external sources only to the Power Inverter Module connector because any circuit fault condition within the Power Inverter Module will cause a complete replacement.

Conditions for Running the DTC

The system voltage is more than 10 V.

The vehicle power mode master requires serial data communication to occur from this specific device.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter device availability has not been received.

Action Taken When the DTC Sets

The device is never signaled. Therefore, the specific subsystems will not function.

Conditions for Clearing the DTC

A current DTC clears when the malfunction is no longer present.

A history DTC clears when the device ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

Diagnostic Aids

Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle

operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

A device on the data communication circuit was disconnected while the communication circuit is awake.

Power to one or more devices was interrupted during diagnosis.

A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold.

Battery power was restored to the vehicle and devices on the communication circuit did not all re- initialize at the same time.

If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

A device may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U-code.

The device may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the non communicating device.

If DTC U1845 or U1846 is only set current in the Hybrid Powertrain Control Module 1, the Power Inverter Module must be replaced due to all circuits between the Hybrid Powertrain Control Module 1 and Motor Control Modules being internal to the Power Inverter Module.

Reference Information

Schematic Reference

Data Communication Schematics Control Module References

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Vehicle in Service Mode.

2. Verify that DTC U0293 is not set.

If DTC U0293 is set

Refer to DTC U0100-U02FF .

If DTC U0293 is not set

3. Verify that DTC U1845 or U1846 is not set current only in the K114A Hybrid Powertrain Control Module 1.

If any of the DTCs are set

Replace the T6 Power Inverter Module.

If none of the DTCs are set

4. All OK.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Serial Data Circuit Wiring Repairs

Control Module References for device replacement, programming and setup

DTC U184A: LOST COMMUNICATION WITH BODY CONTROL MODULE ON LOW SPEED CAN BUS

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach.

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC U184A

Lost Communication with Body Control Module on Low Speed CAN Bus For symptom byte information, refer to Symptom Byte List .

Diagnostic Fault Information

Circuit/System Description

The serial data circuit is the means by which the devices in the vehicle communicate with each other. Once the scan tool is connected to the serial data circuit through the data link connector (DLC), the scan tool can be used to monitor each device for diagnostic purposes and to check for diagnostic trouble codes (DTCs). When the vehicle is ON, each device communicating on the serial data circuit sends a state of health message to ensure that the device is operating properly. When a device stops communicating on the serial data circuit, for example if the device loses power or ground, the state of health message it normally sends on the serial data circuit disappears. Other devices on the serial data circuit, which expect to receive that state of health message, detect its absence; those devices in turn set a DTC associated with the loss of state of health of the non communicating device. A loss of serial data communications DTC does not represent a failure of the devices that contain the stored DTC.

Conditions for Running the DTC

The system voltage is between 9 - 16 V.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter device availability has not been received.

Action Taken When the DTC Sets

The device is never signaled. Therefore, the specific subsystems will not function.

Conditions for Clearing the DTC

A current DTC clears when the malfunction is no longer present.

A history DTC clears when the device ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

Diagnostic Aids

Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves

automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

A device on the data communication circuit was disconnected while the communication circuit is awake.

Power to one or more devices was interrupted during diagnosis.

A low battery condition was present, so some devices stop communicating when battery voltage

drops below a certain threshold.

Battery power was restored to the vehicle and devices on the communication circuit did not all re- initialize at the same time.

If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

A device may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U-code.

Do not replace a device reporting a U-code. The U-code identifies which device needs to be diagnosed for a communication issue.

Communication may be available between the device and the scan tool with one or more GMLAN serial data systems inoperative. This condition is due to the device using multiple GMLAN busses.

Use Data Link References to determine what GMLAN serial data communications the non communicating device uses.

The device may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the non communicating device.

Reference Information

Schematic Reference

Data Communication Schematics Control Module References

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Vehicle in Service Mode.

2. Verify that DTC U0140 is not set.

If DTC U0140 is set

Refer to DTC U0100-U02FF .

If DTC U0140 is not set

3. Verify that DTC U0073, U0078, B1325, B1330, B1370, B1380, B1424, B1428, B1440, B1441, B1517, C0800, C0899, C12E1, P0560, or P0562 is not set.

If any of the DTCs are set

Refer to Diagnostic Trouble Code (DTC) List - Vehicle .

If none of the DTCs are set

4. Refer to Circuit/System Testing.

Circuit/System Testing

NOTE: Use the schematics and connector end views to identify the device's ground, B+, ignition, and serial data circuit terminals.

1. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the harness connectors at the K9 Body Control Module. It may take up to 2 minutes for all vehicle systems to power down.

2. Test for less than 10 Ω between each ground circuit terminal and ground.

If 10 Ω or greater

1. Vehicle OFF.

2. Test for less than 2 Ω in the ground circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, repair the open/high resistance in the ground connection.

If less than 10 Ω

3. Vehicle in Service Mode.

4. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the B+ circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the B+ circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 Body Control Module.

If the test lamp illuminates

5. Vehicle in Service Mode.

6. If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the ignition circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is OK and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the ignition circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 Body Control Module.

If the test lamp illuminates

7. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the harness connectors at the device setting the DTC. It may take up to 2 minutes for all vehicle systems to power down.

8. Test for less than 2 Ω in the low speed GMLAN serial data circuits end to end between the K9 Body Control Module and the device setting the DTC.

If 2 Ω or greater

Repair the open/high resistance in the serial data circuit.

If less than 2 Ω

9. Replace the K9 Body Control Module.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Serial Data Circuit Wiring Repairs

Control Module References for device replacement, programming and setup

DTC U184B: LOST COMMUNICATION WITH REMOTE HEATER AND AIR CONDITIONING CONTROL MODULE ON LOW SPEED CAN BUS

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach.

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC U184B

Lost Communication with Remote Heater and Air Conditioning Control Module on Low Speed CAN Bus

For symptom byte information, refer to Symptom Byte List .

Diagnostic Fault Information

Circuit/System Description

The serial data circuit is the means by which the devices in the vehicle communicate with each other. Once the scan tool is connected to the serial data circuit through the data link connector (DLC), the scan tool can be used to monitor each device for diagnostic purposes and to check for diagnostic trouble codes (DTCs). When the vehicle is ON, each device communicating on the serial data circuit sends a state of health message to ensure that the device is operating properly. When a device stops communicating on the serial data circuit, for example if the device loses power or ground, the state of health message it normally sends on the serial data circuit disappears. Other devices on the serial data circuit, which expect to receive that state of health message, detect its absence; those devices in turn set a DTC associated with the loss of state of health of the non communicating device. A loss of serial data communications DTC does not represent a failure of the devices that contain the stored DTC.

Conditions for Running the DTC

The system voltage is between 9 - 16 V.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter device availability has not been received.

Action Taken When the DTC Sets

The device is never signaled. Therefore, the specific subsystems will not function.

Conditions for Clearing the DTC

A current DTC clears when the malfunction is no longer present.

A history DTC clears when the device ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

Diagnostic Aids

Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of- communication

U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

A device on the data communication circuit was disconnected while the communication circuit is awake.

Power to one or more devices was interrupted during diagnosis.

A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold.

Battery power was restored to the vehicle and devices on the communication circuit did not all re- initialize at the same time.

If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

A device may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U-code.

Do not replace a device reporting a U-code. The U-code identifies which device needs to be diagnosed for a communication issue.

Communication may be available between the device and the scan tool with one or more GMLAN serial data systems inoperative. This condition is due to the device using multiple GMLAN busses.

Use Data Link References to determine what GMLAN serial data communications the non communicating device uses.

The device may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the non communicating device.

Reference Information

Schematic Reference

Data Communication Schematics Control Module References

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Vehicle in Service Mode.

2. Verify that DTC U0164 is not set.

If DTC U0164 is set

Refer to DTC U0100-U02FF .

If DTC U0164 is not set

3. Verify that DTC U0073, U0078, B1325, B1330, B1370, B1380, B1424, B1428, B1440, B1441, B1517, C0800, C0899, C12E1, P0560, or P0562 is not set.

If any of the DTCs are set

Refer to Diagnostic Trouble Code (DTC) List - Vehicle .

If none of the DTCs are set

4. Refer to Circuit/System Testing.

Circuit/System Testing

NOTE: Use the schematics and connector end views to identify the device's ground, B+, ignition, and serial data circuit terminals.

1. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the harness connectors at the K33 HVAC Control Module. It may take up to 2 minutes for all vehicle systems to power down.

2. Test for less than 10 Ω between each ground circuit terminal and ground.

If 10 Ω or greater

1. Vehicle OFF.

2. Test for less than 2 Ω in the ground circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, repair the open/high resistance in the ground connection.

If less than 10 Ω

3. Vehicle in Service Mode.

4. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the B+ circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the B+ circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K33 HVAC Control Module.

If the test lamp illuminates

5. Vehicle in Service Mode.

6. If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the ignition circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is OK and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the ignition circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K33 HVAC Control Module.

If the test lamp illuminates

7. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the harness connectors at the device setting the DTC. It may take up to 2 minutes for all vehicle systems to power down.

8. Test for less than 2 Ω in the low speed GMLAN serial data circuits end to end between the K33 HVAC Control Module and the device setting the DTC.

If 2 Ω or greater

Repair the open/high resistance in the serial data circuit.

If less than 2 Ω

9. Replace the K33 HVAC Control Module.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Serial Data Circuit Wiring Repairs

Control Module References for device replacement, programming and setup

DTC U184C: LOST COMMUNICATION WITH INSTRUMENT CLUSTER ON LOW SPEED CAN BUS

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach.

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC U184C

Lost Communication with Instrument Cluster on Low Speed CAN Bus For symptom byte information, refer to Symptom Byte List .

Diagnostic Fault Information

Circuit/System Description

The serial data circuit is the means by which the devices in the vehicle communicate with each other. Once the scan tool is connected to the serial data circuit through the data link connector (DLC), the scan tool can be used to monitor each device for diagnostic purposes and to check for diagnostic trouble codes (DTCs). When the vehicle is ON, each device communicating on the serial data circuit sends a state of health message to ensure that the device is operating properly. When a device stops communicating on the serial data circuit, for example if the device loses power or ground, the state of health message it normally sends on the serial data circuit disappears. Other devices on the serial data circuit, which expect to receive that state of health message, detect its absence; those devices in turn set a DTC associated with the loss of state of health of the non communicating device. A loss of serial data communications DTC does not represent a failure of the devices that contain the stored DTC.

Conditions for Running the DTC

The system voltage is between 9 - 16 V.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter device availability has not been received.

Action Taken When the DTC Sets

The device is never signaled. Therefore, the specific subsystems will not function.

Conditions for Clearing the DTC

A current DTC clears when the malfunction is no longer present.

A history DTC clears when the device ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

Diagnostic Aids

Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves

automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

A device on the data communication circuit was disconnected while the communication circuit is awake.

Power to one or more devices was interrupted during diagnosis.

A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold.

Battery power was restored to the vehicle and devices on the communication circuit did not all re- initialize at the same time.

If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

A device may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U-code.

Do not replace a device reporting a U-code. The U-code identifies which device needs to be diagnosed for a communication issue.

Communication may be available between the device and the scan tool with one or more GMLAN serial data systems inoperative. This condition is due to the device using multiple GMLAN busses.

Use Data Link References to determine what GMLAN serial data communications the non communicating device uses.

The device may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the non communicating device.

Reference Information

Schematic Reference

Data Communication Schematics Control Module References

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Vehicle in Service Mode.

2. Verify that DTC U0155 is not set.

If DTC U0155 is set

Refer to DTC U0100-U02FF .

If DTC U0155 is not set

3. Verify that DTC U0073, U0078, B1325, B1330, B1370, B1380, B1424, B1428, B1440, B1441, B1517, C0800, C0899, C12E1, P0560, or P0562 is not set.

If any of the DTCs are set

Refer to Diagnostic Trouble Code (DTC) List - Vehicle .

If none of the DTCs are set

4. Refer to Circuit/System Testing.

Circuit/System Testing

NOTE: Use the schematics and connector end views to identify the device's ground, B+, ignition, and serial data circuit terminals.

1. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the harness connectors at the P16 Instrument Cluster. It may take up to 2 minutes for all vehicle systems to power down.

2. Test for less than 10 Ω between each ground circuit terminal and ground.

If 10 Ω or greater

1. Vehicle OFF.

2. Test for less than 2 Ω in the ground circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, repair the open/high resistance in the ground connection.

If less than 10 Ω

3. Vehicle in Service Mode.

4. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the B+ circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the B+ circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the P16 Instrument Cluster.

If the test lamp illuminates

5. Vehicle in Service Mode.

6. If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the ignition circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is OK and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the ignition circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the P16 Instrument Cluster.

If the test lamp illuminates

7. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the harness connectors at the device setting the DTC. It may take up to 2 minutes for all vehicle systems to power down.

8. Test for less than 2 Ω in the low speed GMLAN serial data circuits end to end between the P16 Instrument Cluster and the device setting the DTC.

If 2 Ω or greater

Repair the open/high resistance in the serial data circuit.

If less than 2 Ω

9. Replace the P16 Instrument Cluster.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Serial Data Circuit Wiring Repairs

Control Module References for device replacement, programming and setup

DTC U184D: LOST COMMUNICATION WITH RADIO ON LOW SPEED CAN BUS

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach.

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC U184D

Lost Communication with Radio on Low Speed CAN Bus For symptom byte information, refer to Symptom Byte List .

Diagnostic Fault Information

Circuit/System Description

The serial data circuit is the means by which the devices in the vehicle communicate with each other. Once the scan tool is connected to the serial data circuit through the data link connector (DLC), the scan tool can be used to monitor each device for diagnostic purposes and to check for diagnostic trouble codes (DTCs). When the vehicle is ON, each device communicating on the serial data circuit sends a state of health message to ensure that the device is operating properly. When a device stops communicating on the serial data circuit, for example if the device loses power or ground, the state of health message it normally sends on the serial data circuit disappears. Other devices on the serial data circuit, which expect to receive that state of health message, detect its absence; those devices in turn set a DTC associated with the loss of state of health of the non communicating device. A loss of serial data communications DTC does not represent a failure of the devices that contain the stored DTC.

Conditions for Running the DTC

The system voltage is between 9 - 16 V.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter device availability has not been received.

Action Taken When the DTC Sets

The device is never signaled. Therefore, the specific subsystems will not function.

Conditions for Clearing the DTC

A current DTC clears when the malfunction is no longer present.

A history DTC clears when the device ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

Diagnostic Aids

Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves

automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

A device on the data communication circuit was disconnected while the communication circuit is awake.

Power to one or more devices was interrupted during diagnosis.

A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold.

Battery power was restored to the vehicle and devices on the communication circuit did not all re- initialize at the same time.

If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

A device may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U-code.

Do not replace a device reporting a U-code. The U-code identifies which device needs to be diagnosed for a communication issue.

Communication may be available between the device and the scan tool with one or more GMLAN serial data systems inoperative. This condition is due to the device using multiple GMLAN busses.

Use Data Link References to determine what GMLAN serial data communications the non communicating device uses.

The device may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the non communicating device.

Reference Information

Schematic Reference

Data Communication Schematics Control Module References

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Vehicle in Service Mode.

2. Verify that DTC U0184 is not set.

If DTC U0184 is set

Refer to DTC U0100-U02FF .

If DTC U0184 is not set

3. Verify that DTC U0073, U0078, B1325, B1330, B1370, B1380, B1424, B1428, B1440, B1441, B1517, C0800, C0899, C12E1, P0560, or P0562 is not set.

If any of the DTCs are set

Refer to Diagnostic Trouble Code (DTC) List - Vehicle .

If none of the DTCs are set

4. Refer to Circuit/System Testing.

Circuit/System Testing

NOTE: Use the schematics and connector end views to identify the device's ground, B+, ignition, and serial data circuit terminals.

1. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the harness connectors at the A11 Radio. It may take up to 2 minutes for all vehicle systems to power down.

2. Test for less than 10 Ω between each ground circuit terminal and ground.

If 10 Ω or greater

1. Vehicle OFF.

2. Test for less than 2 Ω in the ground circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, repair the open/high resistance in the ground connection.

If less than 10 Ω

3. Vehicle in Service Mode.

4. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the B+ circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the B+ circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the A11 Radio.

If the test lamp illuminates

5. Vehicle in Service Mode.

6. If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the ignition circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is OK and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the ignition circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the A11 Radio.

If the test lamp illuminates

7. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the harness connectors at the device setting the DTC. It may take up to 2 minutes for all vehicle systems to power down.

8. Test for less than 2 Ω in the low speed GMLAN serial data circuits end to end between the A11 Radio and the device setting the DTC.

If 2 Ω or greater

Repair the open/high resistance in the serial data circuit.

If less than 2 Ω

9. Replace the A11 Radio.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Serial Data Circuit Wiring Repairs

Control Module References for device replacement, programming and setup

DTC U184E: LOST COMMUNICATION WITH INFLATABLE RESTRAINT SENSING AND DIAGNOSTIC MODULE ON LOW SPEED CAN BUS

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach.

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC U184E

Lost Communication with Inflatable Restraint Sensing and Diagnostic Module on Low Speed CAN Bus For symptom byte information, refer to Symptom Byte List .

Diagnostic Fault Information

Circuit/System Description

The serial data circuit is the means by which the devices in the vehicle communicate with each other. Once the scan tool is connected to the serial data circuit through the data link connector (DLC), the scan tool can be used to monitor each device for diagnostic purposes and to check for diagnostic trouble codes (DTCs). When the vehicle is ON, each device communicating on the serial data circuit sends a state of health message to ensure that the device is operating properly. When a device stops communicating on the serial data circuit, for example if the device loses power or ground, the state of health message it normally sends on the serial data circuit disappears. Other devices on the serial data circuit, which expect to receive that state of health message, detect its absence; those devices in turn set a DTC associated with the loss of state of health of the non communicating device. A loss of serial data communications DTC does not represent a failure of the devices that contain the

stored DTC.

Conditions for Running the DTC

The system voltage is between 9 - 16 V.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter device availability has not been received.

Action Taken When the DTC Sets

The device is never signaled. Therefore, the specific subsystems will not function.

Conditions for Clearing the DTC

A current DTC clears when the malfunction is no longer present.

A history DTC clears when the device ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

Diagnostic Aids

Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves

automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

A device on the data communication circuit was disconnected while the communication circuit is awake.

Power to one or more devices was interrupted during diagnosis.

A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold.

Battery power was restored to the vehicle and devices on the communication circuit did not all re- initialize at the same time.

If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

A device may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U-code.

Do not replace a device reporting a U-code. The U-code identifies which device needs to be diagnosed for a communication issue.

Communication may be available between the device and the scan tool with one or more GMLAN serial data systems inoperative. This condition is due to the device using multiple GMLAN busses.

Use Data Link References to determine what GMLAN serial data communications the non communicating device uses.

The device may not have internal protection for specific control circuits and may open a B+ or ignition

fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the non communicating device.

Reference Information

Schematic Reference

Data Communication Schematics Control Module References

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Vehicle in Service Mode.

2. Verify that DTC U0151 is not set.

If DTC U0151 is set

Refer to DTC U0100-U02FF .

If DTC U0151 is not set

3. Verify that DTC U0073, U0078, B1325, B1330, B1370, B1380, B1424, B1428, B1440, B1441, B1517, C0800, C0899, C12E1, P0560, or P0562 is not set.

If any of the DTCs are set

Refer to Diagnostic Trouble Code (DTC) List - Vehicle .

If none of the DTCs are set

4. Refer to Circuit/System Testing.

Circuit/System Testing

NOTE: Use the schematics and connector end views to identify the device's ground, B+, ignition, and serial data circuit terminals.

1. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the harness connectors at the K36 Inflatable Restraint Sensing and Diagnostic Module. It may take up to 2 minutes for all vehicle systems to power down.

2. Test for less than 10 Ω between each ground circuit terminal and ground.

If 10 Ω or greater

1. Vehicle OFF.

2. Test for less than 2 Ω in the ground circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, repair the open/high resistance in the ground connection.

If less than 10 Ω

3. Vehicle in Service Mode.

4. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the B+ circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the B+ circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance, replace the K36 Inflatable Restraint Sensing and Diagnostic Module.

If the test lamp illuminates

5. Vehicle in Service Mode.

6. If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the ignition circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is OK and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the ignition circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance, replace the K36 Inflatable Restraint Sensing and Diagnostic Module.

If the test lamp illuminates

7. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the harness connectors at the device setting the DTC. It may take up to 2 minutes for all vehicle systems to power down.

8. Test for less than 2 Ω in the low speed GMLAN serial data circuits end to end between the K36 Inflatable Restraint Sensing and Diagnostic Module and the device setting the DTC.

If 2 Ω or greater

Repair the open/high resistance in the serial data circuit.

If less than 2 Ω

9. Replace the K36 Inflatable Restraint Sensing and Diagnostic Module.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Serial Data Circuit Wiring Repairs

Control Module References for device replacement, programming and setup

DTC U185A: LOST COMMUNICATION WITH BATTERY ENERGY CONTROL MODULE ON HIGH VOLTAGE ENERGY MANAGEMENT CAN BUS

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach.

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC U185A

Lost Communication with Battery Energy Control Module on High Voltage Energy Management CAN Bus

For symptom byte information, refer to Symptom Byte List .

Diagnostic Fault Information

Circuit/System Description

Devices connected to the serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the devices. The devices have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver device as an availability indication of the transmitter device. Each message contains the identification number of the transmitter device.

Conditions for Running the DTC

The system voltage is more than 10 V.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter device availability has not been received for more than 500 ms.

Action Taken When the DTC Sets DTC U185A is a type A DTC. Conditions for Clearing the DTC DTC U185A is a type A DTC. Diagnostic Aids

Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U code present. However, there is no associated "current" or "active" status. Loss of communication U codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

A device on the data communication circuit was disconnected while the communication circuit is awake.

Power to one or more devices was interrupted during diagnosis.

A low battery condition was present, so some devices stop communicating when battery voltage

drops below a certain threshold.

Battery power was restored to the vehicle and devices on the communication circuit did not all re- initialize at the same time.

If a loss of communication U code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

A device may have a U code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U code.

Do not replace a device reporting a U code. The U code identifies which device needs to be diagnosed for a communication issue.

Communication may be available between the device and the scan tool with one or more GMLAN serial data systems inoperative. This condition is due to the device using multiple GMLAN busses.

Use Data Link References to determine what GMLAN serial data communications the non communicating device uses.

The device may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the non communicating device.

Reference Information

Schematic Reference

Data Communication Schematics

Hybrid/EV Energy Storage Schematics Control Module References

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information Special Tools

EL-48900 HEV Safety Kit

EL-50211 Low Voltage Jumper Harness Extension

For equivalent regional tools, refer to Special Tools .

Circuit/System Verification

1. Vehicle in Service Mode.

2. Verify that DTC U0111 is not set.

If DTC U0111 is set

Refer to DTC U0100-U02FF .

If DTC U0111 is not set

3. Verify that DTC U0073, U0074, U0077, U0078, U007A, P06E4, P1EB9, U1814, U2099, B1325, B1330, B1370, B1380, B1424, B1428, B1440, B1441, B1517, C0800, C0899, C12E1, P0560, or P0562 is not

set.

If any of the DTCs are set

Refer to Diagnostic Trouble Code (DTC) List - Vehicle .

If none of the DTCs are set

4. Refer to Circuit/System Testing.

Circuit/System Testing

WARNING: Always perform the High Voltage Disabling procedure prior to servicing any High Voltage component or connection. Personal Protection Equipment (PPE) and proper procedures must be followed.

The High Voltage Disabling procedure includes the following steps: Identify how to disable high voltage.

Identify how to test for the presence of high voltage.

Identify condition under which high voltage is always present and personal protection equipment (PPE) and proper procedures must be followed.

Before working on any high voltage system, be sure to wear the following Personal Protection Equipment:

Safety glasses with appropriate side shields when within 15 meters (50 feet) of the vehicle, either indoors or outdoors.

Certified and up-to-date Class "0" Insulation gloves rated at 1000V with leather protectors.

Visually and functionally inspect the gloves before use.

Wear the Insulation gloves with leather protectors at all times when working with the high voltage battery assembly, whether the system

is energized or not.

Failure to follow the procedures may result in serious injury or death.

NOTE: Use the schematics and connector end views to identify the device's ground, B+, ignition, accessory wake up serial data 2, high voltage energy management communication enable, and serial data circuit terminals.

1. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 min for all vehicle systems to power down. Disconnect the X357 and X358 harness connectors at the A4 Hybrid/EV Battery Pack.

2. Test for less than 10 Ω between each ground circuit terminal and ground.

If 10 Ω or greater

1. Vehicle OFF.

2. Test for less than 2 Ω in the ground circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, repair the open/high resistance in the ground connection.

If less than 10 Ω

3. Vehicle in Service Mode.

4. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the B+ circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the B+ circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K16 Battery Energy Control Module.

If the test lamp illuminates

5. If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the ignition circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is OK and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the ignition circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K16 Battery Energy Control Module.

If the test lamp illuminates

6. If equipped, verify a test lamp illuminates between the accessory wakeup serial data 2 circuit terminal and ground.

If the test lamp does not illuminate

1. Vehicle OFF, disconnect the X2 harness connector at the K114B Hybrid/EV Powertrain Control Module 2.

2. Test for infinite resistance between the accessory wakeup serial data 2 circuit and ground. If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance

3. Test for less than 2 Ω in the accessory wakeup serial data 2 circuit end to end. If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, replace the K114B Hybrid/EV Powertrain Control Module 2.

If the test lamp illuminates

7. If equipped, verify a test lamp illuminates between the high voltage energy management communication enable circuit terminal and ground.

If the test lamp does not illuminate

1. Vehicle OFF, disconnect the X2 harness connector at the K114B Hybrid/EV Powertrain Control Module 2.

2. Test for infinite resistance between the high voltage energy management communication enable circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance

3. Test for less than 2 Ω in the high voltage energy management communication enable circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, replace the K114B Hybrid/EV Powertrain Control Module 2.

If the test lamp illuminates

8. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 min for all vehicle systems to power down. Disconnect the harness connectors at the device setting the DTC.

9. Test for less than 2 Ω in each high voltage energy management high speed GMLAN serial data circuits end to end between the A4 Hybrid/EV Battery Pack and the device setting the DTC.

If 2 Ω or greater

Repair the open/high resistance in the serial data circuit.

If less than 2 Ω

10. Vehicle OFF, reconnect the X357 and X358 harness connectors at the A4 Hybrid/EV Battery Pack.

11. Perform the High Voltage Disabling procedure before proceeding with this diagnostic. Refer to High

Voltage Disabling .

12. Reconnect the 12 V battery.

13. Vehicle OFF, connect the EL-50211 low voltage jumper harness extension.

14. Disconnect the X8 harness connector at the K16 Battery Energy Control Module.

15. Test for less than 10 Ω between each ground circuit terminal and ground.

If 10 Ω or greater

Repair the open/high resistance in the circuit.

If less than 10 Ω

16. Vehicle in Service Mode.

17. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground.

If the test lamp does not illuminate

Repair the short to ground or the open/high resistance in the circuit.

If the test lamp illuminates

18. If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground.

If the test lamp does not illuminate

Repair the short to ground or the open/high resistance in the circuit.

If the test lamp illuminates

19. If equipped, verify a test lamp illuminates between the accessory wakeup serial data 2 circuit terminal and ground.

If the test lamp does not illuminate

Repair the short to ground or the open/high resistance in the circuit.

If the test lamp illuminates

20. If equipped, verify a test lamp illuminates between the high voltage energy management communication enable circuit terminal and ground.

If the test lamp does not illuminate

Repair the short to ground or the open/high resistance in the circuit.

If the test lamp illuminates

21. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 min for all vehicle systems to power down. Disconnect the X357 harness connector at the A4 Hybrid/EV Battery Pack.

22. Test for less than 2 Ω in each high voltage energy management high speed GMLAN serial data circuits end to end between the K16 Battery Energy Control Module and the A4 Hybrid/EV Battery Pack.

If 2 Ω or greater

Repair the open/high resistance in the circuit.

If less than 2 Ω

23. Replace the K16 Battery Energy Control Module.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Serial Data Circuit Wiring Repairs

Control Module References for device replacement, programming and setup

DTC U185B: BATTERY ENERGY CONTROL MODULE LOST COMMUNICATION WITH HYBRID/EV POWERTRAIN CONTROL MODULE 2 ON HIGH VOLTAGE ENERGY MANAGEMENT CAN BUS

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach.

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC U185B

Battery Energy Control Module Lost Communication with Hybrid/EV Powertrain Control Module 2 on High Voltage Energy Management CAN Bus

For symptom byte information, refer to Symptom Byte List .

Diagnostic Fault Information

Circuit/System Description

Devices connected to the serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the devices. The devices have

prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver device as an availability indication of the transmitter device. Each message contains the identification number of the transmitter device.

This diagnostic is used to check the loss of communication with the Hybrid/EV Powertrain Control Module 2 on high voltage energy management high speed GMLAN bus. The Battery Energy Control Module supervises a periodic serial data message to check the communication status of the Hybrid/EV Powertrain Control Module 2. If this message is not received within 1 s, this DTC is set.

Conditions for Running the DTC

The device is awake and communicating. The system voltage is at least 9 V.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter device availability has not been received within 1 s.

Action Taken When the DTC Sets

No Cell Balancing function. However, cell balancing switch diagnostics still run. DTC U185B is a type B DTC.

Conditions for Clearing the DTC DTC U185B is a type B DTC. Diagnostic Aids

Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U code present. However, there is no associated "current" or "active" status. Loss of communication U codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

A device on the data communication circuit was disconnected while the communication circuit is awake.

Power to one or more devices was interrupted during diagnosis.

A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold.

Battery power was restored to the vehicle and devices on the communication circuit did not all re- initialize at the same time.

If a loss of communication U code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

A device may have a U code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U code.

Do not replace a device reporting a U code. The U code identifies which device needs to be diagnosed for a communication issue.

Communication may be available between the device and the scan tool with one or more GMLAN serial data systems inoperative. This condition is due to the device using multiple GMLAN busses.

Use Data Link References to determine what GMLAN serial data communications the non communicating device uses.

The device may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the non communicating device.

Reference Information

Schematic Reference

Data Communication Schematics Control Module References

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information Special Tools

EL-48900 HEV Safety Kit

For equivalent regional tools, refer to Special Tools .

Circuit/System Verification

1. Vehicle in Service Mode.

2. Verify that DTC U0073, U0074, U0078, U007A, U1814, B1325, B1330, B1370, B1380, B1424, B1428, B1440, B1441, B1517, C0800, C0899, C12E1, P0560, or P0562 is not set.

If any of the DTCs are set

Refer to Diagnostic Trouble Code (DTC) List - Vehicle .

If none of the DTCs are set

3. Refer to Circuit/System Testing.

Circuit/System Testing

WARNING: Always perform the High Voltage Disabling procedure prior to servicing any High Voltage component or connection. Personal Protection Equipment (PPE) and proper procedures must be followed.

The High Voltage Disabling procedure includes the following steps: Identify how to disable high voltage.

Identify how to test for the presence of high voltage.

Identify condition under which high voltage is always present and personal protection equipment (PPE) and proper procedures must be followed.

Before working on any high voltage system, be sure to wear the following Personal Protection Equipment:

Safety glasses with appropriate side shields when within 15 meters (50 feet) of the vehicle, either indoors or outdoors.

Certified and up-to-date Class "0" Insulation gloves rated at 1000V with leather protectors.

Visually and functionally inspect the gloves before use.

Wear the Insulation gloves with leather protectors at all times when working with the high voltage battery assembly, whether the system is energized or not.

Failure to follow the procedures may result in serious injury or death.

NOTE: Use the schematics and connector end views to identify the device's ground, B+, ignition, accessory wake up serial data, and serial data circuit terminals.

1. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 min for all vehicle systems to power down. Disconnect the harness connectors at the K114B Hybrid/EV Powertrain Control Module 2.

2. Test for less than 10 Ω between each ground circuit terminal and ground.

If 10 Ω or greater

1. Vehicle OFF.

2. Test for less than 2 Ω in the ground circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, repair the open/high resistance in the ground connection.

If less than 10 Ω

3. Vehicle in Service Mode.

4. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the B+ circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the B+ circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance, replace the K114B Hybrid/EV Powertrain Control Module 2.

If the test lamp illuminates

5. If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the ignition circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is OK and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the ignition circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance, replace the K114B Hybrid/EV Powertrain Control Module 2.

If the test lamp illuminates

6. If equipped, verify a test lamp illuminates between the accessory wakeup serial data circuit terminal and ground.

If the test lamp does not illuminate

1. Vehicle OFF, disconnect the harness connectors at the K9 Body Control Module.

2. Test for infinite resistance between the accessory wakeup serial data circuit and ground. If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance

3. Test for less than 2 Ω in the accessory wakeup serial data circuit end to end. If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, replace the K9 Body Control Module.

If the test lamp illuminates

7. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 min for all vehicle systems to power down. Disconnect the X357 harness connector at the A4 Hybrid/EV Battery Pack.

8. Test for less than 2 Ω in each high voltage energy management high speed GMLAN serial data circuits end to end between the K114B Hybrid/EV Powertrain Control Module 2 and the A4 Hybrid/EV Battery Pack.

If 2 Ω or greater

Repair the open/high resistance in the serial data circuit.

If less than 2 Ω

9. Vehicle OFF, disable the high voltage system. Refer to High Voltage Disabling .

10. Reconnect the 12 V battery.

11. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 min for all vehicle systems to power down. Disconnect the X8 harness connector at the K16 Battery Energy Control Module.

12. Test for less than 2 Ω in each high voltage energy management high speed GMLAN serial data circuits end to end between the A4 Hybrid/EV Battery Pack and the K16 Battery Energy Control Module.

If 2 Ω or greater

Repair the open/high resistance in the serial data circuit.

If less than 2 Ω

13. Replace the K114B Hybrid/EV Powertrain Control Module 2.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Serial Data Circuit Wiring Repairs

Control Module References for device replacement, programming and setup

DTC U1860: ELECTRIC A/C COMPRESSOR CONTROL MODULE LOST COMMUNICATION WITH HYBRID POWERTRAIN CONTROL MODULE 2

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach.

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC U1860

Electric A/C Compressor Control Module Lost Communication with Hybrid Powertrain Control Module 2

For symptom byte information, refer to Symptom Byte List .

Diagnostic Fault Information

Circuit/System Description

Devices connected to the serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the devices. The devices have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver device as an availability indication of the transmitter device. Each message contains the identification number of the transmitter device.

Conditions for Running the DTC

The system voltage is greater than 10.25 V.

Conditions for Setting the DTC

The A/C Compressor is not able to receive the serial data message from the Hybrid Powertrain Control Module 2 for 3 seconds.

Action Taken When the DTC Sets The DTC U1860 is a type B DTC. Conditions for Clearing the DTC The DTC U1860 is a type B DTC. Diagnostic Aids

Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves

automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

A device on the data communication circuit was disconnected while the communication circuit is awake.

Power to one or more devices was interrupted during diagnosis.

A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold.

Battery power was restored to the vehicle and devices on the communication circuit did not all re- initialize at the same time.

If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

A device may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U-code.

Do not replace a device reporting a U-code. The U-code identifies which device needs to be diagnosed for a communication issue.

Communication may be available between the device and the scan tool with one or more GMLAN serial data systems inoperative. This condition is due to the device using multiple GMLAN busses.

Use Data Link References to determine what GMLAN serial data communications the non communicating device uses.

The device may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the non communicating device.

Reference Information

Schematic Reference

Data Communication Schematics Control Module References

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Vehicle in Service Mode.

2. Verify that DTC U0073, U0074, U0078, U007A, U1814, B1325, B1330, B1370, B1380, B1424, B1428, B1440, B1441, B1517, C0800, C0899, C12E1, P0560, or P0562 is not set.

If any of the DTCs are set

Refer to Diagnostic Trouble Code (DTC) List - Vehicle .

If none of the DTCs are set

3. Refer to Circuit/System Testing.

Circuit/System Testing

NOTE: Use the schematics and connector end views to identify the device's ground, B+, ignition, accessory wake up serial data, and serial data circuit terminals.

1. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the harness connectors at the K114B Hybrid/EV Powertrain Control Module 2. It may take up to 2 minutes for all vehicle systems to power down.

2. Test for less than 10 Ω between each ground circuit terminal and ground.

If 10 Ω or greater

1. Vehicle OFF.

2. Test for less than 2 Ω in the ground circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, repair the open/high resistance in the ground connection.

If less than 10 Ω

3. Vehicle in Service Mode.

4. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the B+ circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the B+ circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance, replace the K114B Hybrid/EV Powertrain Control Module 2.

If the test lamp illuminates

5. Vehicle in Service Mode.

6. If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the ignition circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is OK and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the ignition circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance, replace the K114B Hybrid/EV Powertrain Control Module 2.

If the test lamp illuminates

7. Vehicle in Service Mode.

8. If equipped, verify a test lamp illuminates between the accessory wakeup serial data circuit terminal and ground.

If the test lamp does not illuminate

1. Vehicle OFF, disconnect the harness connectors at the K9 Body Control Module.

2. Test for infinite resistance between the accessory wakeup serial data circuit and ground. If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance

3. Test for less than 2 Ω in the accessory wakeup serial data circuit end to end. If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, replace the K9 Body Control Module.

If the test lamp illuminates

9. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the X1 harness connector at the G1 A/C Compressor. It may take up to 2 minutes for all vehicle systems to power down.

10. Test for less than 2 Ω in each serial data circuits end to end between the K114B Hybrid/EV Powertrain Control Module 2 and the G1 A/C Compressor.

If 2 Ω or greater

Repair the open/high resistance in the serial data circuit.

If less than 2 Ω

11. Replace the K114B Hybrid/EV Powertrain Control Module 2.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Serial Data Circuit Wiring Repairs

Control Module References for device replacement, programming and setup

DTC U1876: DRIVE MOTOR CONTROL MODULE 1 LOST COMMUNICATION WITH ENGINE CONTROL MODULE

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach.

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC U1876

Drive Motor Control Module 1 Lost Communication with Engine Control Module For symptom byte information, refer to Symptom Byte List .

Diagnostic Fault Information

Circuit/System Description

Devices connected to the serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the devices. The devices have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver device as an availability indication of the transmitter device. Each message contains the identification number of the transmitter device.

Conditions for Running the DTC

The system voltage is greater than 9.5 V.

The vehicle power mode master requires serial data communication to occur from this specific device.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter device availability has not been received.

Action Taken When the DTC Sets The DTC U1876 is a type B DTC. Conditions for Clearing the DTC The DTC U1876 is a type B DTC. Diagnostic Aids

Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves

automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

A device on the data communication circuit was disconnected while the communication circuit is awake.

Power to one or more devices was interrupted during diagnosis.

A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold.

Battery power was restored to the vehicle and devices on the communication circuit did not all re- initialize at the same time.

If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

A device may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U-code.

Do not replace a device reporting a U-code. The U-code identifies which device needs to be diagnosed for a communication issue.

Communication may be available between the device and the scan tool with one or more GMLAN serial data systems inoperative. This condition is due to the device using multiple GMLAN busses.

Use Data Link References to determine what GMLAN serial data communications the non communicating device uses.

The device may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the non communicating device.

Reference Information

Schematic Reference

Data Communication Schematics Control Module References

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Vehicle in Service Mode.

2. Verify that DTC U0100 is not set.

If DTC U0100 is set

Refer to DTC U0100-U02FF .

If DTC U0100 is not set

3. Verify that DTC U0073, U0074, U0077, U0078, U007A, P06E4, P1EB9, U1814, U2099, B1325, B1330, B1370, B1380, B1424, B1428, B1440, B1441, B1517, C0800, C0899, C12E1, P0560, or P0562 is not

set.

If any of the DTCs are set

Refer to Diagnostic Trouble Code (DTC) List - Vehicle .

If none of the DTCs are set

4. Refer to Circuit/System Testing.

Circuit/System Testing

NOTE: Use the schematics and connector end views to identify the device's ground, B+, ignition, accessory wake up serial data 2, and serial data circuit terminals.

1. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the harness connectors at the K20 Engine Control Module. It may take up to 2 minutes for all vehicle systems to power down.

2. Test for less than 10 Ω between each ground circuit terminal and ground.

If 10 Ω or greater

1. Vehicle OFF.

2. Test for less than 2 Ω in the ground circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, repair the open/high resistance in the ground connection.

If less than 10 Ω

3. Vehicle in Service Mode.

4. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the B+ circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the B+ circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K20 Engine Control Module.

If the test lamp illuminates

5. Vehicle in Service Mode.

6. If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the ignition circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is OK and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the ignition circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K20 Engine Control Module.

If the test lamp illuminates

7. Vehicle in Service Mode.

8. If equipped, verify a test lamp illuminates between the accessory wakeup serial data 2 circuit terminal and ground.

If the test lamp does not illuminate

1. Vehicle OFF, disconnect the harness connectors at the K114B Hybrid/EV Powertrain Control Module 2.

2. Test for infinite resistance between the accessory wakeup serial data 2 circuit and ground. If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance

3. Test for less than 2 Ω in the accessory wakeup serial data 2 circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, replace the K114B Hybrid/EV Powertrain Control Module 2.

If the test lamp illuminates

9. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the X1 harness connector at the T6 Power Inverter Module. It may take up to 2 minutes for all vehicle systems to power down.

10. Test for less than 2 Ω in each serial data circuits end to end between the K20 Engine Control Module and the T6 Power Inverter Module.

If 2 Ω or greater

Repair the open/high resistance in the serial data circuit.

If less than 2 Ω

11. Replace the K20 Engine Control Module.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Serial Data Circuit Wiring Repairs

Control Module References for device replacement, programming and setup

DTC U1879: DRIVE MOTOR CONTROL MODULE 2 LOST COMMUNICATION WITH ENGINE CONTROL MODULE

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach.

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC U1879

Drive Motor Control Module 2 Lost Communication with Engine Control Module For symptom byte information, refer to Symptom Byte List .

Diagnostic Fault Information

Circuit/System Description

Devices connected to the serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the devices. The devices have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver device as an availability indication of the transmitter device. Each message contains the identification number of the transmitter device.

Conditions for Running the DTC

The system voltage is greater than 9.5 V.

The vehicle power mode master requires serial data communication to occur from this specific device.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter device availability has not been received.

Action Taken When the DTC Sets The DTC U1879 is a type B DTC. Conditions for Clearing the DTC The DTC U1879 is a type B DTC. Diagnostic Aids

Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves

automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

A device on the data communication circuit was disconnected while the communication circuit is awake.

Power to one or more devices was interrupted during diagnosis.

A low battery condition was present, so some devices stop communicating when battery voltage

drops below a certain threshold.

Battery power was restored to the vehicle and devices on the communication circuit did not all re- initialize at the same time.

If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

A device may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U-code.

Do not replace a device reporting a U-code. The U-code identifies which device needs to be diagnosed for a communication issue.

Communication may be available between the device and the scan tool with one or more GMLAN serial data systems inoperative. This condition is due to the device using multiple GMLAN busses.

Use Data Link References to determine what GMLAN serial data communications the non communicating device uses.

The device may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the non communicating device.

Reference Information

Schematic Reference

Data Communication Schematics Control Module References

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Vehicle in Service Mode.

2. Verify that DTC U0100 is not set.

If DTC U0100 is set

Refer to DTC U0100-U02FF .

If DTC U0100 is not set

3. Verify that DTC U0073, U0074, U0077, U0078, U007A, P06E4, P1EB9, U1814, U2099, B1325, B1330, B1370, B1380, B1424, B1428, B1440, B1441, B1517, C0800, C0899, C12E1, P0560, or P0562 is not

set.

If any of the DTCs are set

Refer to Diagnostic Trouble Code (DTC) List - Vehicle .

If none of the DTCs are set

4. Refer to Circuit/System Testing.

Circuit/System Testing

NOTE: Use the schematics and connector end views to identify the device's ground, B+, ignition, accessory wake up serial data 2, and serial data circuit terminals.

1. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the harness connectors at the K20 Engine Control Module. It may take up to 2 minutes for all vehicle systems to power down.

2. Test for less than 10 Ω between each ground circuit terminal and ground.

If 10 Ω or greater

1. Vehicle OFF.

2. Test for less than 2 Ω in the ground circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, repair the open/high resistance in the ground connection.

If less than 10 Ω

3. Vehicle in Service Mode.

4. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the B+ circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the B+ circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K20 Engine Control Module.

If the test lamp illuminates

5. Vehicle in Service Mode.

6. If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the ignition circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is OK and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the ignition circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K20 Engine Control Module.

If the test lamp illuminates

7. Vehicle in Service Mode.

8. If equipped, verify a test lamp illuminates between the accessory wakeup serial data 2 circuit terminal and ground.

If the test lamp does not illuminate

1. Vehicle OFF, disconnect the harness connectors at the K114B Hybrid/EV Powertrain Control Module 2.

2. Test for infinite resistance between the accessory wakeup serial data 2 circuit and ground. If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance

3. Test for less than 2 Ω in the accessory wakeup serial data 2 circuit end to end. If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, replace the K114B Hybrid/EV Powertrain Control Module 2.

If the test lamp illuminates

9. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the X1 harness connector at the T6 Power Inverter Module. It may take up to 2 minutes for all vehicle systems to power down.

10. Test for less than 2 Ω in each serial data circuits end to end between the K20 Engine Control Module and the T6 Power Inverter Module.

If 2 Ω or greater

Repair the open/high resistance in the serial data circuit.

If less than 2 Ω

11. Replace the K20 Engine Control Module.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Serial Data Circuit Wiring Repairs

Control Module References for device replacement, programming and setup

DTC U1885: BATTERY ENERGY CONTROL MODULE LOST COMMUNICATION WITH HYBRID/EV POWERTRAIN CONTROL MODULE

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach.

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC U1885

Battery Energy Control Module Lost Communication with Hybrid/EV Powertrain Control Module For symptom byte information, refer to Symptom Byte List .

Diagnostic Fault Information

Circuit/System Description

Devices connected to the serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the devices. The devices have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver device as an availability indication of the transmitter device. Each message contains the identification number of the transmitter device.

This diagnostic is used to check the loss of communication with Hybrid/EV Powertrain Control Module 1 on high speed GMLAN bus. The Battery Energy Control Module supervises a periodic serial data message to check the communication status of the Hybrid/EV Powertrain Control Module 1. If this message is not received

within 3 s, then this DTC is set.

Conditions for Running the DTC

Vehicle ON.

The system voltage is at least 9 V. The DTC U180B is not set.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter device availability has not been received within 3 s.

Action Taken When the DTC Sets The DTC U1885 is a type B DTC. Conditions for Clearing the DTC The DTC U1885 is a type B DTC. Diagnostic Aids

Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U code present. However, there is no associated "current" or "active" status. Loss of communication U codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

A device on the data communication circuit was disconnected while the communication circuit is awake.

Power to one or more devices was interrupted during diagnosis.

A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold.

Battery power was restored to the vehicle and devices on the communication circuit did not all re- initialize at the same time.

If a loss of communication U code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

A device may have a U code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U code.

Do not replace a device reporting a U code. The U code identifies which device needs to be diagnosed for a communication issue.

Communication may be available between the device and the scan tool with one or more GMLAN serial data systems inoperative. This condition is due to the device using multiple GMLAN busses.

Use Data Link References to determine what GMLAN serial data communications the non communicating device uses.

The device may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the non communicating device.

Reference Information

Schematic Reference

Data Communication Schematics Control Module References

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information Special Tools

EL-48900 HEV Safety Kit

For equivalent regional tools, refer to Special Tools .

Circuit/System Verification

1. Vehicle in Service Mode.

2. Verify that DTC U0293 is not set.

If DTC U0293 is set

Refer to DTC U0100-U02FF .

If DTC U0293 is not set

3. Verify that DTC U0073, U0074, U0077, U0078, U007A, P06E4, P1EB9, U1814, U2099, B1325, B1330, B1370, B1380, B1424, B1428, B1440, B1441, B1517, C0800, C0899, C12E1, P0560, or P0562 is not

set.

If any of the DTCs are set

Refer to Diagnostic Trouble Code (DTC) List - Vehicle .

If none of the DTCs are set

4. Refer to Circuit/System Testing.

Circuit/System Testing

WARNING: Always perform the High Voltage Disabling procedure prior to servicing any High Voltage component or connection. Personal Protection Equipment (PPE) and proper procedures must be followed.

The High Voltage Disabling procedure includes the following steps: Identify how to disable high voltage.

Identify how to test for the presence of high voltage.

Identify condition under which high voltage is always present and personal protection equipment (PPE) and proper procedures must be followed.

Before working on any high voltage system, be sure to wear the following Personal Protection Equipment:

Safety glasses with appropriate side shields when within 15 meters (50 feet) of the vehicle, either indoors or outdoors.

Certified and up-to-date Class "0" Insulation gloves rated at 1000V with leather protectors.

Visually and functionally inspect the gloves before use.

Wear the Insulation gloves with leather protectors at all times when working with the high voltage battery assembly, whether the system is energized or not.

Failure to follow the procedures may result in serious injury or death.

NOTE: Use the schematics and connector end views to identify the device's ground, B+, ignition, accessory wake up serial data 2, and serial data circuit terminals.

1. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. Disconnect the X1 harness connector at the T6 Power Inverter Module. It may take up to 2 min for all vehicle systems to power down.

2. Test for less than 10 Ω between the ground circuit terminal (or T6 Power Inverter Module case) and ground.

If 10 Ω or greater

Check the ground connection and ground strap for the open/high resistance.

If less than 10 Ω

3. Vehicle in Service Mode.

4. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the B+ circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the B+ circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the T6 Power Inverter Module.

If the test lamp illuminates

5. If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF.

2. Test for less than 2 Ω in the ignition circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is OK and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF.

2. Test for infinite resistance between the ignition circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the T6 Power Inverter Module.

If the test lamp illuminates

6. If equipped, verify a test lamp illuminates between the accessory wakeup serial data 2 circuit terminal and ground.

If the test lamp does not illuminate

1. Vehicle OFF, disconnect the harness connectors at the K114B Hybrid/EV Powertrain Control Module 2.

2. Test for infinite resistance between the accessory wakeup serial data 2 circuit and ground. If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance

3. Test for less than 2 Ω in the accessory wakeup serial data 2 circuit end to end. If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, replace the K114B Hybrid/EV Powertrain Control Module 2.

If the test lamp illuminates

7. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. Disconnect the X357 and X358 harness connectors at the A4 Hybrid/EV Battery Pack. It may take up to 2 min for all vehicle systems to power down.

8. Test for less than 2 Ω in each high speed GMLAN serial data circuits end to end between the T6 Power

Inverter Module and the A4 Hybrid/EV Battery Pack.

If 2 Ω or greater

Repair the open/high resistance in the serial data circuit.

If less than 2 Ω

9. Vehicle OFF, disable the high voltage system. Refer to High Voltage Disabling .

10. Reconnect the 12 V battery.

11. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. Disconnect the X8 harness connector at the K16 Battery Energy Control Module. It may take up to 2 min for all vehicle systems to power down.

12. Test for less than 2 Ω in each high speed GMLAN serial data circuits end to end between the A4 Hybrid/EV Battery Pack and the K16 Battery Energy Control Module.

If 2 Ω or greater

Repair the open/high resistance in the serial data circuit.

If less than 2 Ω

13. Replace the T6 Power Inverter Module.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Serial Data Circuit Wiring Repairs

Control Module References for device replacement, programming and setup

DTC U18A2: LOST COMMUNICATION WITH FUEL PUMP DRIVER CONTROL MODULE

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach.

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC U18A2

Lost Communication with Fuel Pump Driver Control Module For symptom byte information, refer to Symptom Byte List .

Diagnostic Fault Information

Circuit/System Description

Devices connected to the serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the devices. The devices have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver device as an availability indication of the transmitter device. Each message contains the identification number of the transmitter device.

Conditions for Running the DTC

The system voltage is between 9 - 16 V.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter device availability has not been received.

Action Taken When the DTC Sets Specific subsystems will not function. Conditions for Clearing the DTC

A current DTC clears when the malfunction is no longer present.

A history DTC clears when the device ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

Diagnostic Aids

Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U code present. However, there is no associated "current" or "active" status. Loss of communication U codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

A device on the data communication circuit was disconnected while the communication circuit is

awake.

Power to one or more devices was interrupted during diagnosis.

A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold.

Battery power was restored to the vehicle and devices on the communication circuit did not all re- initialize at the same time.

If a loss of communication U code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

A device may have a U code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U code.

Do not replace a device reporting a U code. The U code identifies which device needs to be diagnosed for a communication issue.

Communication may be available between the device and the scan tool with one or more GMLAN serial data systems inoperative. This condition is due to the device using multiple GMLAN busses.

Use Data Link References to determine what GMLAN serial data communications the non communicating device uses.

The device may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the non communicating device.

Reference Information

Schematic Reference

Data Communication Schematics Control Module References

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Vehicle in Service Mode.

2. Verify that DTC U0073, U0074, U0075, U0077, U0078, U2100, U1814, U2099, B1325, B1330, B1370, B1380, B1424, B1428, B1440, B1441, B1517, C0800, C0899, C12E1, P0560, or P0562 is not set.

If any of the DTCs are set

Refer to Diagnostic Trouble Code (DTC) List - Vehicle .

If none of the DTCs are set

3. Refer to Circuit/System Testing.

Circuit/System Testing

NOTE: Use the schematics and connector end views to identify the device's ground, B+, ignition, accessory wake up serial data 2, and serial data circuit terminals.

1. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 min for all vehicle systems to power down. Disconnect the harness connectors at the K111 Fuel Pump Driver Control Module.

2. Test for less than 10 Ω between each ground circuit terminal and ground.

If 10 Ω or greater

1. Vehicle OFF.

2. Test for less than 2 Ω in the ground circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, repair the open/high resistance in the ground connection.

If less than 10 Ω

3. Vehicle in Service Mode.

4. If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF, remove the test lamp.

2. Test for less than 2 Ω in the B+ circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF, remove the test lamp.

2. Test for infinite resistance between the B+ circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance, replace the K111 Fuel Pump Driver Control Module.

If the test lamp illuminates

5. Vehicle in Service Mode.

6. If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Vehicle OFF, remove the test lamp.

2. Test for less than 2 Ω in the ignition circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, verify the fuse is OK and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Vehicle OFF, remove the test lamp.

2. Test for infinite resistance between the ignition circuit and ground.

If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance, replace the K111 Fuel Pump Driver Control Module.

If the test lamp illuminates

7. Vehicle in Service Mode.

8. If equipped, verify a test lamp illuminates between the accessory wakeup serial data 2 circuit terminal and ground.

If the test lamp does not illuminate

1. Vehicle OFF, remove the test lamp, disconnect the harness connectors at the K114B Hybrid/EV Powertrain Control Module 2.

2. Test for infinite resistance between the accessory wakeup serial data 2 circuit and ground. If less than infinite resistance, repair the short to ground on the circuit.

If infinite resistance

3. Test for less than 2 Ω in the accessory wakeup serial data 2 circuit end to end. If 2 Ω or greater, repair the open/high resistance in the circuit.

If less than 2 Ω, replace the K114B Hybrid/EV Powertrain Control Module 2.

If the test lamp illuminates

9. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 min for all vehicle systems to power down. Disconnect the harness connectors at the device setting the DTC.

10. Test for less than 2 Ω in each serial data circuits end to end between the K111 Fuel Pump Driver Control Module and the device setting the DTC.

If 2 Ω or greater

Repair the open/high resistance in the serial data circuit.

If less than 2 Ω

11. Replace the K111 Fuel Pump Driver Control Module.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Serial Data Circuit Wiring Repairs

Control Module References for device replacement, programming and setup

DTC U18B5: LOST COMMUNICATION WITH HYBRID POWERTRAIN CONTROL MODULE ON CHASSIS EXPANSION CAN BUS

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach.

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC U18B5

Lost Communication With Hybrid Powertrain Control Module on Chassis Expansion CAN Bus For symptom byte information, refer to Symptom Byte List .

Diagnostic Fault Information

Circuit/System Description

Devices connected to the Chassis high speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the devices. The devices have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver device as an availability indication of the transmitter device. Each message contains the identification number of the transmitter device.

The Motor Control Modules and the Hybrid Powertrain Control Module 1 are all internal to the Power Inverter Module. Communication diagnostics for the serial data, including device power and ground as well as the wakeup circuits for Motor Control Modules and the Hybrid Powertrain Control Module 1 are all diagnosed from external sources only to the Power Inverter Module connector because any circuit fault condition within the Power Inverter Module will cause a complete replacement.

Conditions for Running the DTC

The system voltage is between 9 - 16 V.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter device availability has not been received.

Action Taken When the DTC Sets

The device is never signaled. Therefore, the specific subsystems will not function.

Conditions for Clearing the DTC

A current DTC clears when the malfunction is no longer present.

A history DTC clears when the device ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

Diagnostic Aids

Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U code present. However, there is no associated "current" or "active" status. Loss of communication U codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

A device on the data communication circuit was disconnected while the communication circuit is awake.

Power to one or more devices was interrupted during diagnosis.

A low battery condition was present, so some devices stop communicating when battery voltage drops below a certain threshold.

Battery power was restored to the vehicle and devices on the communication circuit did not all re- initialize at the same time.

If a loss of communication U code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

A device may have a U code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U code.

Do not replace a device reporting a U code. The U code identifies which device needs to be diagnosed for a communication issue.

Communication may be available between the device and the scan tool with one or more GMLAN serial data systems inoperative. This condition is due to the device using multiple GMLAN busses.

Use Data Link References to determine what GMLAN serial data communications the non communicating device uses.

The device may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the non communicating device.

Reference Information

Schematic Reference

Data Communication Schematics Control Module References

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Ignition ON/Vehicle in Service Mode.

2. Verify that DTC U0293 is not set.

If DTC U0293 is set

Refer to DTC U0100-U02FF .