Automatic Transmission

DTC U0121: ABS/ASC-ECU Time Out

DESCRIPTIONS OF MONITOR METHODS

- Open circuit or short circuit occurs in the CAN communication line (CAN_H, CAN_L).

- Reception from ABS/ASC-ECU becomes impossible for 0.5 seconds or more.

TROUBLESHOOTING HINTS (THE MOST LIKELY CAUSES FOR THIS CODE TO BE SET ARE:)

- Damaged harness or connector

- Malfunction of the CAN communication

- Malfunction of the ABS/ASC-ECU

- Malfunction of the TCM

DIAGNOSIS

STEP 1. Check the CAN communication system malfunction.

- Check that the CAN system-related DTC code other than U0121 is set.

- Check if the CAN-related DTC is set with ABS/ASC-ECU.

- Check if the failure related to the ABS/ASC occurs.

Q. Is the check result normal?

YES Go to Step 2.
NO Repair or replace the failure section.
STEP 2. Check the CAN communication lines.

[C-38 TCM connector (vehicle side, disconnected)]

Between C-38 terminal No. 10, 11 and the CAN communication lines of ABS/ASC-ECU: Continuity exists.

When the continuity check result is OK, check that the wiring harness is not shorted to the body and other wiring harness. Also, check for a short circuit between the twisted pair cables.

Q. Is the check result normal?

YES Go to Step 3.
NO Repair or replace the failure section.
STEP 3. Check the ABS/ASC-ECU, the TCM connector pin terminal, and the connection status.

Q. Is the check result normal?

YES Repair or replace the failure section.
NO Replace the TCM.