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

NOTE:  Before you troubleshoot, review the General Troubleshooting Information - Refer to: HOW TO TROUBLESHOOT THE FUEL AND EMISSIONS SYSTEMS or How to Troubleshoot the CVT System(CVT) .

DTC (CVT)

1. PGM-FI system DTC check:

   - 1. Turn the vehicle to the ON mode.

   - 2. Clear the DTC with the HDS.

   - 3. Check for Pending or Confirmed DTCs in the PGM-FI system with the HDS.

   DTC Description	Confirmed DTC	Pending DTC	Freeze Frame
   U0121 F-CAN Malfunction (PCM-ABS Modulator-Control Unit)

   Is DTC U0121 indicated in the PGM-FI system?

   YES 

   Go to the troubleshooting for DTC U0121 in the PGM-FI system - Refer to: DTC Troubleshooting: U0121(CVT),  or DTC Troubleshooting: U0121(PGM-FI System) .

   NO 

   Go to step 2.

2. Problem verification:

   - 1. Check for Pending or Confirmed DTCs in the CVT system with the HDS.

   DTC Description	Confirmed DTC	Pending DTC	Freeze Frame
   U0121 Lost Communication With Anti-Lock Brake System (ABS) Control Module

   Is DTC U0121 indicated in the CVT system?

   YES 

   The failure is duplicated. Update the PCM if it does not have the latest software , or substitute a known-good PCM , then recheck. If DTC U0121 goes away and the PCM was updated, troubleshooting is complete. If DTC U0121 goes away and the PCM was substituted, replace the original PCM .

   NO 

   Intermittent failure, the system is OK at this time. Check for poor connections and loose terminals between the ABS modulator-control unit and the PCM. If the freeze data/on-board snapshot of this DTC is recorded, try to reproduce the failure under the same conditions with the freeze data/on-board snapshot.