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
  • The diagnosis code setting enabled signal is received from ETACS-ECU.
Judgment Criterion
  • The signals cannot be received from ASC-ECU for 0.5 seconds or more.

FAIL-SAFE AND BACKUP FUNCTION



  • None

COMMENT ON TROUBLE SYMPTOM


Current malfunction
  • The failure is possibly caused by malfunction of the harness and connector in CAN bus line between engine-ECU and ASC-ECU, by malfunction in the power supply system of ASC-ECU, in ASC-ECU itself, in engine-ECU.
Past malfunction
  • Proceed with troubleshooting focusing on malfunction of the harness and connector in CAN bus line between engine-ECU and ASC-ECU and malfunction in the power supply system of ASC-ECU. For diagnosis procedure, refer to how to cope with past malfunctions (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Treat Past Trouble ).
    note In the case of past malfunctions, M.U.T.-III CAN bus line diagnosis cannot detect a malfunction even if there is a malfunction in CAN bus. Therefore, check CAN bus line as in the case of response to intermittent malfunctions (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ). It is possible to narrow down areas with a high possibility of malfunctions from diagnosis codes stored in each ECU that performs CAN communication (Refer to GROUP 54C - Explanation about the M.U.T.-III CAN Bus Diagnostics ).

PROBABLE CAUSES



  • Failed of the harness and the connector
  • Failed engine-ECU
  • Failed ASC-ECU

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.