DTC Troubleshooting: U0121
DTC U0121: Lost Communication With Anti-Lock Brake System (ABS) Control Module
NOTE: Before you troubleshoot, review the General Troubleshooting Information.

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

1.
PGM-FI system DTC check:

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
     
     
     
     
NO
     
     
     
Go to step 2.
2.
Problem verification:

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.?