DTC U0401: Engine signal malfunction detected: 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

1. 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? 

   1. YES:  Go to Step 2.
   2. NO:  Repair the CAN bus lines (Refer to CAN BUS DIAGNOSTICS TABLE ). On completion, go to  Step 5.
2. 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? 

   1. YES:  Troubleshoot the relevant DTC, and then go to  Step 5.
   2. NO:  Go to Step 3.
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? 

   1. YES:  Troubleshoot the relevant DTC, and then go to  Step 5.
   2. NO:  Go to Step 4.
4. STEP 4. Check whether the DTC is reset. 

   Erase the DTC.

   Q: Is DTC U0401 set? 

   1. YES:  Replace the hydraulic unit (integrated with ASC-ECU) (Refer to HYDRAULIC UNIT  ), and then go to Step 5.
   2. NO:  Intermittent malfunction (Refer to HOW TO COPE WITH INTERMITTENT MALFUNCTIONS ).
5. STEP 5. Check whether the DTC is reset. 

   Erase the DTC.

   Q: Is DTC U0401 set? 

   1. YES:  Return to  Step 1.
   2. NO:  The procedure is complete.