U0401

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 Diagnostic trouble code diagnosis Diagnostic Trouble Code Descriptions).
^ 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. Using scan tool MB991958, diagnose the CAN bus lines.
Use scan tool to diagnose the CAN bus lines.
Q: Is the check result normal?
YES: Go to Step 2.
NO: Repair the CAN bus lines (Refer to Diagnosis - CAN Bus Diagnostic Table CAN Bus Diagnostics Table). On completion, go to Step 5.

STEP 2. Using scan tool MB991958, check the DTC
Use scan tool to check that any DTC other than the DTC U0401 is set in ASC-ECU.
Q: Is the DTC set?
YES: Troubleshoot the relevant DTC, and then go to Step 5.
NO: Go to Step 3.

STEP 3. Using scan tool MB991958, check the other system DTC
Use scan tool to check that the DTC is set by the engine control module (ECM).
Q: Is the DTC set?
YES: Troubleshoot the relevant DTC, and then go to Step 5.
NO: Go to Step 4.

STEP 4. Check whether the DTC is reset.
Q: Is DTC U0401 set?
YES: Replace the hydraulic unit (ASC-ECU), and then go to Step 5.
NO: Intermittent malfunction.

STEP 5. Check whether the DTC is reset.
Q: Is DTC U0401 set?
YES: Return to Step 1.
NO: The procedure is complete.