Code No. U0121: ASC-ECU Time-out



caution If Diagnosis Code U0121 is stored in the engine-ECU surely perform CAN bus line diagnosis.
caution Replace ECU after certainly confirming that the communication circuits are normal.

TROUBLE JUDGMENT


Check Condition
Judgment Criterion

FAIL-SAFE AND BACKUP FUNCTION




COMMENT ON TROUBLE SYMPTOM


Current malfunction
Past malfunction

PROBABLE CAUSES




DIAGNOSIS PROCEDURE


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



  • Using M.U.T.-III, perform CAN bus line diagnosis.

Q. Is the check result normal?

Go to Step 2.
Correct CAN bus line (Refer to GROUP 54C - Troubleshooting - CAN Bus Diagnostics Table ), and then go to Step 4.

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



  • Confirm whether the diagnosis codes are set from ASC-ECU.

Q. Is the diagnosis code set?

Perform the troubleshooting of ASC system (Refer to GROUP 35C - Troubleshooting - Diagnosis Code Chart ).
Go to Step 3.

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


Check that the other ECU performing CAN communication with ASC-ECU sets diagnosis code No. U0121 [Refer to GROUP 54C - CAN communication-related Diagnosis Code Table ].

Q. Is the diagnosis code set?

Go to Step 4.
Go to Step 5.

STEP 4. M.U.T.-III diagnosis code



  • Reconfirm whether the diagnosis codes are set from engine-ECU

  1. Erase the diagnosis codes being set.
  2. Ignition switch: "LOCK" (OFF) to ON
  3. Confirm whether the diagnosis codes are set.

Q. Is the diagnosis code set?

Go to Step 5.
Intermittent malfunction in CAN bus line between engine-ECU and ASC-ECU (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction ).

STEP 5. Replace the ASC-ECU



  • After replacing the ASC-ECU, re-check the diagnosis code set.

Q. Is the diagnosis code set?

Replace the engine-ECU.
The check is end.