DTC U0121: F-CAN Malfunction (PCM-ABS Modulator-Control Unit)

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 (see DTC U0029: F-CAN MALFUNCTION (BUS-OFF (PCM)) ).

   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 system with the HDS.

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

   YES  -Go to step  6.

   NO  -Go to symptom troubleshooting for ABS indicator, brake system indicator do not go off (see SYMPTOM TROUBLESHOOTING INDEX ).

6. Turn the ignition switch to LOCK (0).
7. Jump the SCS line with the HDS.
8. Disconnect the ABS modulator-control unit 47P connector.
9. Disconnect PCM connector A (44P).
10. Check for continuity between PCM connector terminal A36 and ABS modulator-control unit 47P connector terminal No. 12.
    Fig 1: Checking Continuity Between PCM Connector Terminal A36 And ABS Modulator-Control Unit 47P Connector Terminal No. 12

    Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there continuity? 

    YES  -Go to step  11.

    NO  -Repair an 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 47P connector terminal No. 13.
    Fig 2: Checking Continuity Between PCM Connector Terminal A37 And ABS Modulator-Control Unit 47P Connector Terminal No. 13

    Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there continuity? 

    YES  -Substitute a known-good ABS modulator-control unit (see ABS MODULATOR-CONTROL UNIT REMOVAL AND INSTALLATION ), then go to step  12 and recheck. If DTC U0121 is not indicated after substitution, replace the original ABS modulator-control unit (see ABS MODULATOR-CONTROL UNIT REMOVAL AND INSTALLATION ), then go to step  12.

    NO  -Repair an 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 (see 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 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.