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DTC U0401 Engine signal malfunction detected


caution
  • If there is any problem in the CAN bus lines, an incorrect DTC may be set. Prior to this diagnosis, diagnose the CAN bus lines (Refer to GROUP 54C - Diagnostic trouble code diagnosis ).
  • If DTC U0401 is set in ASC-ECU, always diagnose the CAN bus line. If there is any fault in the CAN bus lines, an incorrect DTC may be set. In this case, the set DTC 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 control module (ECM) via CAN bus lines.

DTC SET CONDITIONS
This DTC is set when the engine control module (ECM) malfunction has been detected.

PROBABLE CAUSES

  • Malfunction of engine system
  • Malfunction of engine control module (ECM)
  • Malfunction of ASC-ECU
  • External noise interference

DIAGNOSIS
Required Special Tools:
  • MB991958: Scan Tool (M.U.T.-III Sub Assembly)

    • MB991824: Vehicle Communication Interface (V.C.I.)
    • MB991827: M.U.T.-III USB Cable
    • MB991910: M.U.T.-III Main Harness A

STEP 1. M.U.T.-III CAN bus diagnosis
Use scan tool 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 - CAN Bus Diagnostic table ). On completion, go to Step 5.

STEP 2. M.U.T.-III DTC
Use scan tool to check that any DTC other than the DTC U0401 is set in ASC-ECU.

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

STEP 3. M.U.T.-III other system DTC
Use scan tool to check that the DTC is set by the engine control module (ECM).

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

STEP 4. Check whether the DTC is reset.

Q. Is DTC U0401 set?
Replace the hydraulic unit (ASC-ECU) (Refer to ), and then go to Step 5.
Intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent Malfunction ).

STEP 5. Check whether the DTC is reset.

Q. Is DTC U0401 set?
Return to Step 1.
The procedure is complete.