Code No.U0121: ABS/ASC CAN Timeout

  • If there is any problem in the CAN bus lines, an incorrect diagnosis code may be set. Prior to this diagnosis, diagnose the CAN bus lines.
  • Whenever the ECU is replaced, ensure that the CAN bus lines are normal.



  • The signal sent from the ASC-ECU cannot be received for a certain period.


  • Malfunction of the CAN bus line
  • Malfunction of ASC-ECU
  • Malfunction of ACC/FCM-ECU


STEP 1. M.U.T.-III CAN bus diagnostics.

Use M.U.T.-III to perform the CAN bus diagnosis.

Q. Is the check result normal?

Go to Step 2
Repair the CAN bus lines (Refer to GROUP 54C - Troubleshooting ).

STEP 2. M.U.T.-III other system diagnosis code.

Check the ASC diagnosis code (Refer to GROUP 35C - Troubleshooting ).

Q. Is the diagnosis code set?

Perform the relevant troubleshooting.
Go to Step 3

STEP 3. M.U.T.-III other system diagnosis code.

Check if the diagnosis code No. U0121 is set to other ECU.

Q. Is the diagnosis code set?

Replace the hydraulic unit (integrated with ASC-ECU) (Refer to GROUP 35C - Hydraulic Unit ).
Go to Step 4

STEP 4. Check whether the diagnosis code is reset.

Q. Is diagnosis code No.U0121 set?

Replace the ACC/FCM-ECU (Refer to ).
Intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent Malfunction ).