Code No. U0121: ABS-ECU/ASTC-ECU time-out


caution
  • If diagnosis code U0121 is set in the A/T-ECU, always diagnose the CAN main bus line.
  • Whenever the ECU is replaced, ensure that the communication circuit is normal.

DIAGNOSIS CODE SET CONDITIONS


If signals from the ABS-ECU/ASTC-ECU transmitted via CAN bus line cannot be received, code No.U0121 is set.

PROBABLE CAUSES



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 whether the diagnosis code is set in the ABS-ECU/ASTC-ECU.

Q. Is diagnosis code set?
YES <Vehicles with ABS> : Perform troubleshooting of the anti-lock brake system (ABS) (Refer to GROUP 35B - Diagnosis Code Chart ).
YES <Vehicles with ASTC> : Perform troubleshooting of ASTC 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 ABS-ECU/ASTC-ECU 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 whether the diagnosis code is set in the A/T-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/ASTC-ECU, go to Step 6.
Intermittent malfunction in CAN bus line between A/T-ECU and ABS-ECU/ASTC-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 whether the diagnosis code is set in the A/T-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 A/T-ECU, go to Step 6.
Intermittent malfunction in CAN bus line between A/T-ECU and ABS-ECU/ASTC-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 whether the diagnosis code is set in the A/T-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.