Code No. U0401 Engine malfunction detected


caution
  • If there is any problem in the CAN bus lines, an incorrect diagnosis code may be set. Prior to this diagnosis, diagnose the CAN bus lines (Refer to GROUP 54C, Trouble code diagnosis ).
  • If diagnosis code U0401 is set in ASC-ECU, always diagnose the CAN bus line. If there is any fault in the CAN bus lines, an incorrect diagnosis code may be set. In this case, the set diagnosis code is not highly reliable.
  • Before replacing the ECU, ensure that the communication circuit is normal.

OPERATION
Engine-related signals are sent or received to and from between ASC-ECU and engine ECU via CAN bus lines.

DIAGNOSIS CODE SET CONDITIONS
This diagnosis code is set when the engine ECU malfunction has been detected.

PROBABLE CAUSES

  • Engine ECU malfunction
  • ASC-ECU malfunction
  • External noise interference

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III CAN bus diagnosis
Use M.U.T.-III to diagnose the CAN bus lines.

Q. Is the check result normal?
Go to Step 2.
Repair the CAN bus lines (Refer to GROUP 54C - Troubleshooting ). On completion, go to Step 5.

STEP 2. M.U.T.-III diagnosis code
Use M.U.T.-III to check that any diagnosis code other than the code No. U0401 is set in ASC-ECU.

Q. Is the diagnosis code set?
Troubleshoot the relevant diagnosis code, and then go to Step 5.
Go to Step 3.

STEP 3. M.U.T.-III other system diagnosis code
Use M.U.T.-III to check that the diagnosis code is set by the engine ECU.

Q. Is the diagnosis code set?
Troubleshoot the relevant diagnosis code, and then go to Step 5.
Go to Step 4.

STEP 4. Check whether the diagnosis code is reset.

Q. Is the diagnosis code No. U0401 set?
Replace the ASC-ECU.
If the trouble symptom is resolved, an intermittent malfunction such as poorly engaged connector(s) or wiring harness is suspected (Refer to GROUP 00 - How to Cope with Intermittent Malfunction ).

STEP 5. Check whether the diagnosis code is reset.

Q. Is the diagnosis code No. U0401 set?
Return to Step 1.
This diagnosis is complete.