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

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 (PGM-FI)

1. Problem verification:

   - 1. Turn the vehicle to the ON mode.

   - 2. Clear the DTC with the HDS.

   - 3. Check for Pending or Confirmed DTCs with the HDS.

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

   Is DTC U0121 indicated?

   YES 

   The failure is duplicated. Go to step 2.

   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. 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.

2. ABS check:

   - 1. Check for communication to the ABS with the HDS.

   Does the HDS communicate with the ABS?

   YES 

   Go to step 3.

   NO 

   Refer to: ABS indicator, brake system indicator (red), and VSA indicator do not go off (VSA System Components) .

3. Open wire check (F-CAN_H line):

   - 1. Turn the vehicle to the OFF (LOCK) mode.

   - 2. Jump the SCS line with the HDS.

   SCS Short

   - 3. Disconnect the following connectors.

   PCM connector A (51P)

   ABS modulator-control unit 38P connector

   - 4. Check for continuity between test points 1 and 2.

   Test condition	Vehicle OFF (LOCK) mode
   	PCM connector A (51P): disconnected
   	ABS modulator-control unit 38P connector: disconnected
   Test point 1	ABS modulator-control unit 38P connector No. 38. Refer to figure below.
   Test point 2	PCM connector A (51P) No. 2

   Is there continuity?

   YES 

   The F-CAN_H wire is OK. Go to step 4.

   NO 

   Repair an open in the F-CAN_H wire between the PCM (A2) and the ABS modulator-control unit.

4. Open wire check (F-CAN_L line):

   - 1. Check for continuity between test points 1 and 2.

   Test condition	Vehicle OFF (LOCK) mode
   	PCM connector A (51P): disconnected
   	ABS modulator-control unit 38P connector: disconnected
   Test point 1	ABS modulator-control unit 38P connector No. 26. Refer to figure below.
   Test point 2	PCM connector A (51P) No. 1

   Is there continuity?

   YES 

   The F-CAN_L wire is OK. Replace the ABS MODULATOR-CONTROL UNIT ABS modulator-control unit.

   NO 

   Repair an open in the F-CAN_L wire between the PCM (A1) and the ABS modulator-control unit.

Courtesy of AMERICAN HONDA MOTOR CO., INC.