DTC U0401: Engine CAN data error: Diagnosis

Required Special Tools: 

• MB991958: Scan Tool (M.U.T.-III Sub Assembly)
  • MB991824: Vehicle Communication Interface
  • MB991827: M.U.T.-III USB Cable
  • MB991910: M.U.T.-III Main Harness A

1. STEP 1. Scan tool MB991958 CAN bus diagnostics 

   Use scan tool MB991958 to diagnose the CAN bus lines.

   Q: Is the check result normal? 

   1. YES:  Go to Step 2.
   2. NO:  Repair the CAN bus line (Refer to CAN BUS DIAGNOSTICS TABLE ). Then go to Step 2.
2. STEP 2. Scan tool MB991958 data list 

   Check the following data list (Refer to DATA LIST REFERENCE TABLE  ).

   • Item 08: CAN data (Engine)

   Q: Is the check result normal? 

   1. YES:  Go to  Step 7.
   2. NO:  Go to Step 3.
3. STEP 3. Scan tool MB991958 DTC of other systems 

   Check if a DTC related to the accelerator pedal position sensor system or the crank angle sensor system is set in the engine control system.

   Q: Is the DTC set? 

   1. YES:  Troubleshoot the engine control system (Refer to DIAGNOSTIC TROUBLE CODE CHART < 4B12 >).
   2. NO:  Go to Step 4.
4. STEP 4. Scan tool MB991958 DTC of other systems 

   Check if a DTC, which relates to the CAN communication-linked systems below, is set.

   • Meter

     U0401: DTC of engine-related failure information

   Q: Is the DTC set? 

   1. YES:  Go to Step 5.
   2. NO:  Go to  Step 6.
5. STEP 5. Check whether the DTC is reset. 

   Q: Is the DTC U0401 set? 

   1. YES:  Replace the engine control module (Refer to ENGINE CONTROL MODULE < 4B12 >). Then go to  Step 7.
   2. NO:  A poor connection, open circuit or other intermittent malfunction between the engine control module and the accelerator pedal position sensor, or between the engine control module and the crank angle sensor is suspected (Refer to HOW TO COPE WITH INTERMITTENT MALFUNCTIONS ). Then to Step 6.
6. STEP 6. Check whether the DTC is reset. 
   1. Erase the DTC.
   2. Turn the ignition switch from the "LOCK" (OFF) position to the "ON" position.
   3. Depress the throttle pedal fully.
   4. Check if the DTC is set.

   Q: Is the DTC U0401 set? 

   1. YES:  Replace AWD-ECU (Refer to AWD-ECU  ). Then go to Step 7.
   2. NO:  A poor connection, open circuit or other intermittent malfunction between the engine control module and the accelerator pedal position sensor, or between the engine control module and the crank angle sensor is suspected (Refer to HOW TO COPE WITH INTERMITTENT MALFUNCTION ).
7. STEP 7. Check whether the DTC is reset. 

   Q: Is the DTC U0401 set? 

   1. YES:  Diagnose again from  Step 1.
   2. NO:  The procedure is complete.