DTC Troubleshooting: U0121 (107-7)

DTC U0121:  Lost Communication with ABS Modulator-Control Unit

NOTE: Before you troubleshoot, record all freeze data and any on-board snapshot, and review General Troubleshooting Information.

1.Clear the DTC with the HDS.

2.Turn the ignition switch ON (II).

3.Check that DTC U0121 recurs.

Is DTC U0121 indicated?


YES - Go to 4.


NO - Intermittent failure, the system is OK at this time.n


4.Check whether any DTC is indicated in the DTCs/Freeze Data in ABS Mode Menu with the HDS.

Is any DTC indicated in the ABS?


YES - Troubleshoot for indicated DTC in the ABS.


NO - Go to 5.


5.Turn the ignition switch OFF.

6.Jump the SCS line with the HDS.

7.Disconnect PCM connector A (44P).

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

9.Check for continuity between PCM connector terminal A36 and ABS modulator-control unit 25P connector terminal No. 1, and between A37 and terminal No. 17.

 

Is there continuity?


YES - Update the PCM if it does not have the latest software, or substitute a known-good PCM, then recheck. If the symptom/indication goes away with a known-good PCM, replace the original  PCM.n


NO - Go to 10.


10.Check the communication line between the ABS modulator-control unit and gauge control module by the HDS.

Is there malfunction in the F-CAN line between the ABS modulator-control unit and gauge control module?


YES - Repair open in the wires between ABS modulator-control unit 25P connector and CAN communication lines.n


NO - Substitute a known-good ABS modulator-control unit, then recheck. If the symptom/indication goes away with a known-good ABS modulator-control unit, replace the original  ABS modulator-control unit.n