U0121

LOST COMMUNICATION WITH ANTI-LOCK BRAKE MODULE

For a complete wiring diagramRefer to Section 8WWhen Monitored:Continuously while the system is active.Set Condition:The ECM doesn’t receive a Bus Message from the Anti-lock Brake Module.

Possible CausesINTERMITTENT DTCCAN BUS OPEN OR SHORTED CONDITIONANTI-LOCK BRAKE MODULEENGINE CONTROL MODULE (ECM)

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.(Refer to 9 – ENGINE – DIAGNOSIS AND TESTING)Diagnostic Test

1. DTC IS ACTIVEIgnition on, engine not running.With the scan tool, clear DTCs in the Engine Control Module (ECM).Monitor the scan tool for at least two minutes.Cycle the ignition key off and on several times, leaving the ignition on for at least 10 seconds at a time.Start the engine.Allow the engine to reach normal operating temperature.With the scan tool, select View DTCs.Is the status Active for this DTC?YesRefer to

8 – ELECTRICAL/ELECTRONIC CONTROL MODULES – DIAGNOSIS AND TESTING for diagnostic procedures and for further possible causes.NoRefer to the *CHECKING FOR AN INTERMITTENT DTC Diagnostic Procedure.(Refer to

9 – ENGINE – DIAGNOSIS AND TESTING)