PGM-FI System

DTC Troubleshooting: U0121, U0121

DTC U0121:

F-CAN Malfunction (ECM/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 U0029 and U0121 indicated at the same time?

YES -

Go to the troubleshooting for DTC U0029 PGM-FI System.

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 ECM/PCM.

5. Check for communication to the ABS system 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. Symptom Related Diagnostic Procedures

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 ECM/PCM connector A (49P).

10. Check for continuity between ECM/PCM connector terminal A3 and ABS modulator-control unit 25P connector terminal No. 1.





Is there continuity?

YES -

Go to step 11.

NO -

Repair an open in the wire between the ECM/PCM(A3) and the ABS modulator-control unit, then go to step 12.

11. Check for continuity between ECM/PCM connector terminal A4 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 an open in the wire between the ECM/PCM(A4) 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 ECM/PCM with the HDS.

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

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

Is DTC U0121 indicated?

YES -

Check for poor connections or loose terminals at the gauge control module, the ABS modulator-control unit, and the ECM/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.