Body Control System

U0121-LOST COMMUNICATION WITH ANTI-LOCK BRAKE SYSTEM (ABS) CONTROL MODULE

U0121 - Lost Communication With Anti-lock Brake System (ABS) Control Module:

WHEN MONITORED
- With the ignition on
- Battery voltage between 10 and 16 volts
- IOD fuse installed

SET CONDITION
Bus messages not received from the Antilock Brake Module for approximately 500ms.

POSSIBLE CAUSES
- CAN C BUS circuits open or shorted
- DTCs related to battery voltage, ignition, or VIN messages
- Antilock brake module
- Antilock brake module power and ground
- Module that set this DTC

DIAGNOSTIC TEST

1. VERIFY DTC IS ACTIVE

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

Turn the ignition on.
With the scan tool, read active DTCs.

Q: Is this DTC active?

YES: Go To 2
NO: Perform the Stored Lost Communication test procedure. Stored Lost Communication DTCs

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

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

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

YES: Diagnose and repair the DTC.
NO: Go To 3

3. VERIFY THAT THE ABS MODULE IS ACTIVE ON THE BUS
With the scan tool, select ECU View.
Verify that the ABS is active on the bus.

Q: Is the ABS active on the bus?

YES: Go To 4
NO: Refer to Body Control Systems for No Response diagnostic procedures.

4. CHECK FOR ADDITIONAL COMMUNICATION RELATED DTCS
With the scan tool, select Network View and select Advanced.

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

YES: Replace/update the Antilock Brake Module.
Perform BODY VERIFICATION TEST - VER 1. Body Verification Test
NO: Replace/update the module that set this DTC.
Perform BODY VERIFICATION TEST - VER 1. Body Verification Test