Transmission
DTC U0121: Lost Communication with ABS Modulator-Control UnitNOTE: 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 step 4.
NO - Intermittent failure, the system is OK at this time.
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 the indicated ABS DTC.
NO - Go to step 5.
5. Turn the ignition switch OFF.
6. Jump the SCS line with the HDS.
7. Disconnect PCM connector E (31 P).
8. Disconnect the ABS modulator-control unit 25P connector.
9. Check for continuity between PCM connector terminal E11 and ABS modulator-control unit 25P connector terminal No. 1, and between PCM connector terminal E24 and ABS modulator-control unit 25P connector 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 for DTC U0121. If the symptom/indication goes away with a known-good PCM, replace the original PCM.
NO - Go to step 10.
10. Check the communication line between the ABS modulator-control unit and the gauge control module by the HDS.
Is there a malfunction in the F-CAN line between the ABS modulator-control unit and the gauge control module?
YES - Repair open in the wires between ABS modulator-control unit 25P connector and the F-CAN communication lines.
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.