U0121

DTC Troubleshooting: U0121

DTC U0121:

F-CAN Malfunction (PCM-ABS Modulator-Control Unit)

NOTE: Before you troubleshoot, record all freeze data and any on-board snapshot, and review the general troubleshooting information Initial Inspection and Diagnostic Overview.

1. Turn the ignition switch to ON (II).

2. Check for Pending or Confirmed DTCs with the HDS.

Are DTC U0028 and U0121 indicated at the same time?

YES -

Go to troubleshooting for DTC U0028 .�

NO -

Go to step 3.

3. Clear the DTC with the HDS.

4. Check for Pending or Confirmed DTCs with the HDS.

Is DTC U0121 indicated?

YES -

Go to step 5.

NO -

Intermittent failure, the system is OK at this time. Check for poor connections or loose terminals at the ABS modulator-control unit, and the PCM.�

5. Check for communication to the ABS with the HDS.

Does the HDS communicate with the ABS modulator-control unit?

YES -

Go to step 6.

NO -

Go to the symptom troubleshooting for ABS indicator and brake system indicator do not go off .�

6. Turn the ignition switch to LOCK (0).

7. Jump the SCS line with the HDS.

8. Disconnect the ABS modulator-control unit 25P connector.

9. Disconnect PCM connector A (44P)

10. Check for continuity between PCM connector terminal A36 and ABS modulator-control unit 25P connector terminal No. 1.





Is there continuity?

YES -

Go to step 11.

NO -

Repair open in the wire between the PCM (A36) and the ABS modulator-control unit, then go to step 12.

11. Check for continuity between PCM connector terminal A37 and ABS modulator-control unit 25P connector terminal No. 17.





Is there continuity?

YES -

Substitute a known-good ABS modulator-control unit, then go to step 12 and recheck. If DTC U0121 is not indicated after substitution, replace the original ABS modulator-control unit, then go to step 12.

NO -

Repair open in the wire between the PCM (A37) and the ABS modulator-control unit, then go to step 12.

12. Reconnect all connectors.

13. Turn the ignition switch to ON (II).

14. Reset the PCM with the HDS.

15. Do the PCM idle learn procedure PCM Idle Learn Procedure.

16. Check for Pending or Confirmed DTCs with the HDS.

Is DTC U0121 indicated?

YES -

If DTC U0121 indicated, check for poor connections or loose terminals at the ABS modulator-control unit and the PCM, then go to step 1.

NO -

Troubleshooting is complete. If any other Pending or Confirmed DTCs are indicated, go to the indicated DTC's troubleshooting.�