Code No. U0121: ASC-ECU Time-out



caution If diagnosis code U0121 is set from AS&G-ECU, surely perform CAN bus line diagnosis.
caution Replace ECU after certainly confirming that the communication circuits are normal.

TROUBLE JUDGMENT


Check Conditions
  • 2 seconds later after the ignition switch has been in "ON" position or the engine has started up.
  • The battery voltage is more than 9 V and is less than 16 V.
Judgement Criterion
  • Unable to receive the signals from the ASC-ECU for 4 seconds.

COMMENTS ON TROUBLE SYMPTOM


Current malfunction
  • The failure is possibly caused by malfunction of the harness and connector in CAN bus line between AS&G-ECU and ASC-ECU, by malfunction in the power supply system of ASC-ECU, in ASC-ECU itself, in AS&G-ECU.
Past malfunction
  • Proceed with troubleshooting focusing on malfunction of the harness and connector in CAN bus line between AS&G-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 set to each ECU that performs CAN communication (Refer to GROUP 54C - Explanation about the M.U.T.-III CAN Bus Diagnostics).
FAIL-SAFE AND BACKUP FUNCTION
  • In the normal operation, the auto stop is prohibited.
  • If the malfunction is detected during the auto stop, the auto start is prohibited.

PROBABLE CAUSES



  • Failed harness and connector
  • Failed ASC-ECU
  • Failed AS&G-ECU

DIAGNOSIS PROCEDURE


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


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

Q. Is the check result normal?

Go to Step 2.
Repair CAN bus line (Refer to GROUP 54C - Troubleshooting - CAN Bus Diagnosis Chart ). After repairing CAN bus line, go to Step 6.

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


Confirm the diagnosis code is set from the ASC-ECU.

Q. Is the diagnosis code set?

Perform troubleshooting of the ASC-ECU (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 (U-code) Table ).

Q. Is the diagnosis code set?

Go to Step 4.
Go to Step 5.

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



  • Reconfirmation of diagnosis code.
Confirm again the diagnosis code is set from the AS&G-ECU.

  1. Erase the set diagnosis code.
  2. Ignition switch: "LOCK" (OFF) → "ON"
  3. Confirm whether the diagnosis code is set.

Q. Is the diagnosis code set?

After replacing the ASC-ECU, go to Step 6.
Intermittent malfunction in CAN bus line between AS&G-ECU and ASC-ECU (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions).

STEP 5. M.U.T.-III diagnosis code



  • Reconfirmation of diagnosis code.
Confirm again the diagnosis code is set from the AS&G-ECU.

  1. Erase the set diagnosis code.
  2. Ignition switch: "LOCK" (OFF) → "ON"
  3. Confirm whether the diagnosis code is set.

Q. Is the diagnosis code set?

After replacing the AS&G-ECU, go to Step 6.
Intermittent malfunction in CAN bus line between AS&G-ECU and ASC-ECU (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions).

STEP 6. M.U.T.-III diagnosis code



  • Reconfirmation of diagnosis code.
Confirm again the diagnosis code is set from the AS&G-ECU.

  1. Erase the set diagnosis code.
  2. Ignition switch: "LOCK" (OFF) → "ON"
  3. Confirm whether the diagnosis code is set.

Q. Is the diagnosis code set?

Go to Step 1.
Check end.