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U007A




DTC U007A

Diagnostic Instructions

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

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

* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC U007A
- Control Module Communication High Voltage Energy Management CAN Bus Off

For symptom byte information, refer to Symptom Byte List Symptom Byte List.

Diagnostic Fault Information






Circuit/System Description

Devices connected to the high voltage energy management high speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the devices when the vehicle is on. The high voltage energy management high speed GMLAN serial data bus uses a terminating resistor that is in parallel with the high voltage energy management high speed GMLAN (+) and (-) circuits.

The high voltage energy management high speed GMLAN serial data circuits connect directly to the auxiliary data connector. The scan tool does not communicate with high voltage energy management high speed GMLAN bus.

Conditions for Running the DTC

* Supply voltage to the devices are in the normal operating range.

* The vehicle power mode requires serial data communications.

Conditions for Setting the DTC

The device setting the DTC has attempted to establish communications on the high voltage energy management high speed GMLAN serial data circuits more than 3 times.

Action Taken When the DTC Sets

* The device suspends all message transmission.

* The device uses default values for all parameters received on the serial data circuits.

* The device inhibits the setting of all other communication DTCs.

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, 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.

* 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.

* The engine may not start when there is a total malfunction of the high voltage energy management high speed GMLAN serial data bus.

* Use Data Link References Initial Inspection and Diagnostic Overview to determine which devices connect to the high voltage energy management high speed GMLAN serial data bus.

Reference Information

Schematic Reference

* Data Communication Schematics [1][2]Electrical Diagrams

* Control Module References Programming and Relearning

Connector End View Reference

Component Connector End Views Hybrid/EV Battery Pack X1

Description and Operation

Data Link Communications Description and Operation Description and Operation

Electrical Information Reference

* Circuit Testing Circuit Testing

* Connector Repairs Connector Repairs

* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections

* Wiring Repairs Wiring Repairs

Scan Tool Reference

Control Module References Programming and Relearning for scan tool information

Special Tools

EL-48900 - HEV Safety Kit

For equivalent regional tools, refer to Special Tools Tools and Equipment.

Circuit/System Testing

Danger: 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.


Danger: The Volt Battery Pack will utilize an exchange program. Please consult the most recent revision of bulletin/PI #PIP4841, available in Service Information (SI), for a list of approved Volt Battery Pack service procedures. Components that may be removed and serviced without exchanging the complete battery pack are identified in the bulletin/PI. Please contact the GM Technical Assistance Center if you have any questions.


Note: Some devices with an internal terminating resistor have a loop in the harness that connects the internal terminating resistor to the serial data circuit. When wired this way, test these loop circuits for the appropriate failure mode short to voltage, short to ground, or open/high resistance prior to replacing the device for each of the following tests.

Each device may need to be disconnected to isolate
a circuit fault. Use the schematics and connector end views to identify the following:

* High voltage energy management high speed GMLAN devices the vehicle is equipped with

* High voltage energy management high speed GMLAN serial data circuit terminating resistors

* Device locations on the high voltage energy management high speed GMLAN serial data circuits

* Each device's ground, B+, ignition, and high voltage energy management high speed GMLAN serial data circuit terminals

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

2. Reconnect the 12 V battery after performing the high voltage disabling procedure.

3. Vehicle in Service Mode.

4. Verify two or more devices are not communicating on the high voltage energy management high speed GMLAN serial data circuit. Refer to Data Link References Initial Inspection and Diagnostic Overview to determine how many devices should be communicating on the bus.

• If only one device is not communicating
Refer to Testing the Device Circuits.

• If two or more devices are not communicating

5. 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 scan tool from the X84 data link connector. The following tests will be done at the X84B auxiliary data connector. It may take up to 2 minutes for all vehicle systems to power down.

6. Test for less than 10 ohms between the ground circuit terminal 5 and ground.

• If 10 ohms or greater

1. Vehicle OFF.

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

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

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

• If less than 10 ohms

7. Vehicle in Service Mode.

8. Test for less than 4.5 V between the serial data circuits listed below and ground.

* Terminal 3

* Terminal 11

• If 4.5 V or greater
Refer to Testing the Serial Data Circuits for a Short to Voltage.

• If less than 4.5 V

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

10. Test for greater than 100 ohms between the serial data circuits listed below and ground.

* Terminal 3

* Terminal 11

• If 100 ohms or less
Refer to Testing the Serial Data Circuits for a Short to Ground.

• If greater than 100 ohms

11. Test for 50-70 ohms between the serial data circuit terminals 3 and 11.

• If less than 35 ohms
Refer to Testing the Serial Data Circuits for a Short between the Circuits.

• If between 35-50 ohms
There may be a third terminating resistor between the serial data circuits. This can happen if the incorrect device is installed. Some devices are available with and without the terminating resistors installed to reduce the need of terminating resistors in the wiring harness. Refer to Testing the Serial Data Circuits for a Short between the Circuits.

• If greater than 70 ohms but less than infinite
Refer to Testing the Serial Data Circuits for an Open/High Resistance.

• If infinite resistance
Repair the open/high resistance in the circuit between the X84B auxiliary data connector and the first splice/device in the serial data circuit.

• If between 50-70 ohms

12. Refer to Testing the Device Circuits.

Testing the Serial Data Circuits for a Short to Voltage

1. Vehicle OFF, disconnect the harness connectors with the high voltage energy management high speed GMLAN serial data circuits at an easily accessible device, Vehicle in Service Mode.

2. Test for greater than 4.5 V between each serial data circuit at the device connector that was just disconnected and ground.

• If each serial data circuit is 4.5 V or less

1. Vehicle OFF.

2. Test for less than 10 ohms between each of the device's ground circuit terminals and ground.

• If 10 ohms or greater, repair the open/high resistance in the circuit.

• If less than 10 ohms, replace the device that was disconnected.

• If any serial data circuit is greater than 4.5 V

3. Vehicle OFF, disconnect the harness connectors with the high voltage energy management high speed GMLAN serial data circuits at another device, in the direction of the circuit shorted to voltage, Vehicle in Service Mode.

4. Test for greater than 4.5 V between each serial data circuit at the device connector that was just disconnected and ground.

• If each serial data circuit is 4.5 V or less

1. Vehicle OFF.

2. Test for less than 10 ohms between each of the device's ground circuit terminals and ground.

• If 10 ohms or greater, repair the open/high resistance in the circuit.

• If less than 10 ohms, replace the device that was disconnected.

• If any serial data circuit is greater than 4.5 V

5. Repeat step 3 until one of the following conditions are isolated:

* A short to voltage on the serial data circuit between two devices or splice packs, if equipped.

* A short to voltage on the serial data circuit between a device and a terminating resistor.

Testing the Serial Data Circuits for a Short to Ground

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

2. Disconnect the harness connectors with the high voltage energy management high speed GMLAN serial data circuits at an easily accessible device.

3. Test for greater than 100 ohms between each serial data circuit at the device connector that was just disconnected and ground.

• If each serial data circuit is 100 ohms or greater
Replace the device that was disconnected.

• If any serial data circuit is less than 100 ohms

4. Disconnect the harness connectors with the high voltage energy management high speed GMLAN serial data circuits at another device, in the direction of the circuit shorted to ground.

5. Test for greater than 100 ohms between each serial data circuit at the device connector that was just disconnected and ground.

• If both serial data circuits are 100 ohms or greater
Replace the device that was disconnected.

• If any serial data circuit is less than 100 ohms

6. Repeat step 4 until one of the following conditions are isolated:

* A short to ground on the serial data circuit between two devices or splice packs, if equipped.

* A short to ground on the serial data circuit between a device and a terminating resistor.

* A short to ground on the serial data circuit between the X84B auxiliary data connector and the first device or splice pack.

Testing the Serial Data Circuits for a Short between the Circuits

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

2. Disconnect the harness connectors with the high voltage energy management high speed GMLAN serial data circuits at an easily accessible device that is not communicating.

3. Test for greater than 110 ohms between each pair of serial data circuits at the device connector that was just disconnected.

• If each pair of serial data circuits is 110 ohms or greater
Replace the device that was disconnected.

• If any pair of serial data circuits is less than 110 ohms

4. Connect the harness connectors at the device that was disconnected.

5. Disconnect the harness connectors with the high voltage energy management high speed GMLAN serial data circuits at another device, in the direction of the circuit shorted together.

6. Test for greater than 110 ohms between each pair of serial data circuits at the device connector that was just disconnected.

• If each pair of serial data circuits is 110 ohms or greater
Replace the device that was disconnected.

• If any pair of serial data circuits is less than 110 ohms

7. Repeat step 4 until one of the following conditions are isolated:

* Serial data circuits shorted together between two devices or splice packs, if equipped.

* Serial data circuits shorted together between a device and a terminating resistor.

* Serial data circuits shorted together between the X84B auxiliary data connector and the first device or splice pack.

* A shorted terminating resistor.

Testing the Serial Data Circuits for an Open/High Resistance

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

2. Disconnect the harness connectors with the high voltage energy management high speed GMLAN serial data circuits at an easily accessible device that is not communicating.

3. Test for less than 130 ohms between each pair of serial data circuits at the device connector that was just disconnected.

• If each pair of serial data circuit is 130 ohms or less
Replace the device that was disconnected.

• If any pair of serial data circuits is greater than 130 ohms

4. Connect the harness connectors at the device that was disconnected.

5. Disconnect the harness connectors with the high voltage energy management high speed GMLAN serial data circuits at another device, in the direction of the circuit with the open/high resistance.

6. Test for less than 130 ohms between each pair of serial data circuits at the device connector that was just disconnected.

• If each pair of serial data circuits is 130 ohms or less
Replace the device that was disconnected.

• If any pair of serial data circuits is greater than 130 ohms

7. Repeat step 4 until one of the following conditions are isolated:

* An open/high resistance on the serial data circuit between two devices or splice packs, if equipped.

* An open/high resistance on the serial data circuit between a device and a terminating resistor.

* An open/high resistance terminating resistor.

Testing the Device Circuits

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

2. Disconnect the harness connectors at an easily accessible device that is not communicating.

3. Test for less than 10 ohms between each ground circuit terminal and ground.

• If 10 ohms or greater

1. Vehicle OFF.

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

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

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

• If less than 10 ohms

4. Vehicle in Service Mode

5. 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 ohms in the B+ circuit end to end.

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

• If less than 2 ohms, 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 disconnected device.

• If the test lamp illuminates

6. Vehicle in Service Mode.

7. If equipped, verify a test lamp illuminates between each ignition circuit terminal, which has a fuse in the circuit, and ground.

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

1. Vehicle OFF.

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

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

• If less than 2 ohms, 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 disconnected device.

• If the test lamp illuminates

8. Vehicle in Service Mode

9. If equipped, verify a test lamp illuminates between each ignition circuit terminal, which is controlled by a control module, and ground.

• If the test lamp does not illuminate

1. Vehicle OFF, disconnect the harness connectors at the control module that controls the ignition circuit.

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

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

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

• If less than 2 ohms, replace the control module that controls the ignition circuit.

• If the test lamp illuminates

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

11. Test for less than 130 ohms between each pair of high voltage energy management high speed GMLAN serial data circuits at the device connector that was just disconnected.

• If any pair of serial data circuits is greater than 130 ohms
Repair the open/high resistance in the serial data circuits between the disconnected device and the circuit splice in the serial data circuits.

• If each pair of serial data circuits is 130 ohms or less

12. Replace the device that was disconnected.

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the repair.

* GMLAN Wiring Repairs GMLAN Wiring Repairs

* Control Module References Programming and Relearning for device replacement, programming and setup

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