Code No.U0401 Engine revolution data input malfunction


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.
  • Whenever ECU is replaced, ensure that the CAN bus lines are normal.

OPERATION

  • Electric power steering-ECU receives engine revolution signal from the engine-ECU.

FUNCTION

  • The engine speed signal is sent to the electric power steering-ECU for motor control.

TROUBLE JUDGEMENT
Check Conditions
  • The power supply circuit system diagnosis code (No. C1540, C1541) is not set.
  • The engine circuit system diagnosis code is not set.
Judgement Criterion
  • Abnormal engine speed signal sent to the electric power steering-ECU is received once or more.
  • The abnormal engine speed signal is sent from the engine-ECU, and the microcomputer determines that there is a problem in the engine speed measurement system.
Fail Safe, Back Up Function
  • The electric power steering-ECU illuminates the electric power steering warning display, and sets the diagnosis code No. U0401. Normally the assist operation is continued while the vehicle is driven, but deactivated after the vehicle stopped.

PROBABLE CAUSES

  • Malfunction of CAN bus line
  • Malfunction of the electric power steering-ECU
  • Malfunction of the engine-ECU

DIAGNOSIS PROCEDURE

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

Q. Is the check result normal?
Go to Step 3.
Repair the CAN bus lines (Refer to GROUP 54C - Troubleshooting ). On completion, go to Step 2.

STEP 2. Diagnosis code recheck after resetting CAN bus lines
(1)Erase the diagnosis code.
(2)Turn the ignition switch from the LOCK (OFF) position to the ON position.
(3)Check if the diagnosis code is set.

Q. Is the diagnosis codes U0401 set?
Go to Step 3.
This diagnosis is complete.

STEP 3. M.U.T.-III data list
Check the following service data .

  • Item No. 07: Engine speed

Q. Is the check result normal?
Go to Step 5.
Perform troubleshooting for engine-ECU (Refer to GROUP 13A - Troubleshooting . Then go to Step 4.

STEP 4. Check whether the diagnosis code is reset
(1)Erase the diagnosis code.
(2)Turn the ignition switch from the LOCK (OFF) position to the ON position.
(3)Check if the diagnosis code is set.

Q. Is the diagnosis codes U0401 set?
Replace the electric power steering-ECU (Refer to ).Then go to Step 5.
Intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent Malfunction ).

STEP 5. Check whether the diagnosis code is reset.
(1)Erase the diagnosis code.
(2)Turn the ignition switch from the LOCK (OFF) position to the ON position.
(3)Check if the diagnosis code is set.

Q. Is the diagnosis codes U0401 set?
Return to Step 1.
This diagnosis is complete.