U0121

U0121-LOST COMMUNICATION WITH ANTI-LOCK BRAKE MODULE





For a complete wiring diagram, refer to the Wiring Information.

- When Monitored:
With the ignition on.

Battery voltage between 10 and 16 volts.

Ignition Off Draw (IOD) fuse installed.

Front Control Module (FCM) is configured correctly.

- Set Condition:
Bus messages not received from the Antilock Brake Module for approximately two to five seconds.





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

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

1. Using the scan tool, read active DTCs.

Is this DTC active?

Yes

- Go To 2

No

- Perform the Stored Lost Communication DTCs diagnostic procedure. Stored Lost Communication DTCs

2. CHECK FOR ANY OF THE FOLLOWING ACTIVE DTCS
1. Using 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. Using 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 from ABS diagnostic procedure. No Response From ABS (Antilock Brake Module)

4. CHECK FOR ADDITIONAL COMMUNICATION RELATED DTCS
1. Using 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 ABS VERIFICATION TEST. ABS Verification Test

No

- Replace/update the module that set this DTC
- Perform the appropriate verification test for the module being replaced. If there is no verification test for the associated module perform the BODY VERIFICATION TEST. Body Verification Test.