Code No. U0121: ABS-ECU or ASC-ECU Time-out


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

TROUBLE JUDGMENT


Check Conditions
  • After 2 seconds have passed since the ignition switch was turned to "ON" position.
  • Battery positive voltage is 10 V or higher.
Judgment Criterion
  • Unable to receive ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC> signals through the CAN busline for 4 seconds.

COMMENTS ON TROUBLE SYMPTOM


Current malfunction
  • The failure is possibly caused by malfunction of the harness and connector in CAN busline 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 busline 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 Malfunctions ).
    note In the case of past malfunctions, M.U.T.-III CAN busline diagnosis cannot detect a malfunction even if there is a malfunction in CAN bus. Therefore, check CAN busline 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 output to each ECU that performs CAN communication (Refer to GROUP 54C - Explanation about the M.U.T.-III CAN Bus Diagnostics ).

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 busline diagnosis.

Q. Is the check result normal?
Go to Step 2 .
Repair CAN busline (Refer to GROUP 54C - Troubleshooting - CAN Bus Diagnosis Table ). After repairing CAN busline, go to Step 6 .

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

  • Confirm the diagnosis code is outputted from the ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC>.

Q. Is diagnosis code set?
Perform troubleshooting of ABS or ASC (Refer to GROUP 35B <Vehicles with ABS> - Troubleshooting - Diagnosis Code Chart ) or GROUP 35C <Vehicles with ASC> - Troubleshooting - Diagnosis Code Chart ).
Go to Step 3 .

STEP 3. M.U.T.-III diagnosis code
Diagnosis code No. U0121 from the following ECU that performs CAN communication with ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC>: Confirm ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC> Time-out is output.

  • A/T-ECU
  • 4WD-ECU

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 outputted from the engine-ECU.

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

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 busline 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 outputted from the engine-ECU.

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

Q. Is diagnosis code set?
After replacing the engine-ECU, go to Step 6 .
Intermittent malfunction in CAN busline 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 outputted from the engine-ECU.

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

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