Powertrain Control Module (PCM)

U0121-LOST COMMUNICATION WITH ANTI-LOCK BRAKE MODULE





For a complete wiring diagramrefer to the Wiring Information Electrical Diagrams.

- When Monitored:
Ignition run time is greater than 1 second. Battery voltage between 9 and 16 volts. Engine run time greater than 3 seconds.

- Set Condition:
The PCM doesn't receive an ABS message over the CAN C circuit for 7 consecutive seconds. The circuit is continuously monitored. One trip fault.





WARNING: On vehicles equipped with the high voltage system, you must thoroughly read and follow all High Voltage Safety procedures. In addition, before performing any diagnostic or service procedure near a high voltage component, you must perform the High Voltage Power Down. Failure to follow these instructions may result in possible serious or fatal injury

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure.

1. VERIFY THE DIAGNOSTIC TROUBLE CODE (DTC) IS ACTIVE

NOTE: Ensure the IOD fuse is installed and battery voltage is between 10 and 16 volts before proceeding.

1. With the scan tool, read active DTCs.

Is this DTC active?

Yes

- Go To 2

No

- Refer to the Stored Lost Communication test procedure. Stored Lost Communication DTCs

2. CHECK FOR ANY OF THE FOLLOWING ACTIVE DTCS
1. With the scan tool, read all active DTCs from all modules.

NOTE: Check for FCM configuration, CAN B or C hardware electrical, VIN Missing/Mismatch, battery or ignition related DTCs.

Does the scan tool display any active DTCs to the conditions listed above?

Yes

- Go to and perform the appropriate diagnostic procedure.

No

- Go To 3

3. VERIFY THAT THE ABS IS ACTIVE ON THE BUS
1. Turn the ignition on.
2. With the scan tool, select Network Diagnostics.
3. Verify that the ABS is active on the bus.

Is the ABS active on the bus?

Yes

- Go To 4

No

- Perform the No Response diagnostic procedure. Manufacturer Code Charts

4. CHECK FOR ADDITIONAL COMMUNICATION RELATED DTCS
1. With the scan tool, select Network Diagnostics.

Is there more than one module with active DTCs "Logged Against" the ABS?

Yes

- Replace/update the Antilock Brake Module.
- Perform the BODY VERIFICATION TEST. Body Verification Test

No

- Replace/update the module that set this DTC
- Perform the BODY VERIFICATION TEST. Body Verification Test