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 (Refer to GROUP 54C, CAN Bus Diagnostics Table).
  • Whenever ECU is replaced, ensure that the CAN bus lines are normal.

OPERATION

    EPS-ECU receives engine revolution signal from the engine-ECU.

FUNCTION

    The engine speed signal is sent to the EPS-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
    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 EPS-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 EPS-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 - CAN Bus Diagnostics Table ). 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/Inspection Chart for Diagnosis code <1600 Petrol>, GROUP 13D - Troubleshooting/Inspection Chart for Diagnosis code <1800, 2000 Petrol>, GROUP 13B - Troubleshooting/Inspection Chart for Diagnosis code <Diesel>. 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 EPS-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.