Code No. U0121: ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC> Time-out


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

TROUBLE JUDGMENT


Check Conditions
  • More than 2 seconds have passed since the ignition switch was turned to "ON" position.
  • Battery positive voltage is more than 10 V and is less than 16 V.
Judgement Criterion
  • Unable to receive ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC> signals through the CAN bus line 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 engine-ECU and ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC>, by malfunction in the power supply system of ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC>, in ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC> 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 ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC> and malfunction in the power supply system of ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC>.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



  • None

PROBABLE CAUSES



  • Failed harness and connector
  • Failed ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC>
  • Failed engine-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 Diagnostics Table ). 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 ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC>.

Q. Is diagnosis code set?
Perform troubleshooting of the anti-lock brake system (ABS) or the active stability control (ASC) system (Refer to GROUP 35B - Troubleshooting <Vehicles with ABS>, Refer to GROUP 35C - Troubleshooting - Diagnosis Code Chart <Vehicles with ASC>).
Go to Step 3.

STEP 3. M.U.T.-III diagnosis code
Check that the other ECU performing CAN communication with ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC> sets diagnosis code No. U0121 [Refer to GROUP 54C - CAN Communication-related Diagnosis Code (U-code) Table ].

Q. Is 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 engine-ECU.

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

Q. Is diagnosis code set?
After replacing ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC>, go to Step 6.
Intermittent malfunction in CAN bus line between engine-ECU and ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC> (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 engine-ECU.

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

Q. Is diagnosis code set?
After replacing engine-ECU, go to Step 6.
Intermittent malfunction in CAN bus line between engine-ECU and ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC> (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 engine-ECU.

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

Q. Is diagnosis code set?
Go to Step 1.
Check end.