Body Control System

U0121-LOST COMMUNICATION WITH ANTI-LOCK BRAKE MODULE

U0121-Lost Communication With Anti-Lock Brake Module:

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

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

POSSIBLE CAUSES
- CAN B or CAN C BUS circuits open or shorted
- DTCs related to battery voltage, ignition, or VIN messages
- FCM not configured correctly
- Antilock brake module power and ground
- Antilock brake module
- 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.

With the scan tool, read active DTCs.

Q: Is this DTC active?

YES: Go To 2
NO: Refer to the Stored Lost Communication test procedure. Perform BODY VERIFICATION TEST - VER 1. Body Verification Test

2. CHECK FOR ANY OF THE FOLLOWING ACTIVE DTCs
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.

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

YES: Diagnose and repair the DTC. Perform BODY VERIFICATION TEST - VER 1. Body Verification Test
NO: Go To 3

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

Q: Is the ABS active on the bus?

YES: Go To 4
NO: Refer to no response test procedure. Perform BODY VERIFICATION TEST - VER 1. Body Verification Test

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

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