Inspection Procedure 1: Scan tool MB991958 cannot Communicate with the Electronic Control AWD System: 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 ). On completion, go to Step 2.
2. STEP 2. Check the following connector: 

   Check the connectors below for improper engagement, terminal damage or terminal drawn in the connector case.

   • C-57 AWD-ECU connector
   • C-309, C-313 ETACS-ECU connector
   • D-52 joint connector (2)

   Q: Are the connectors and terminals in good condition? 

   1. YES:  Go to Step 3.
   2. NO:  Repair the connector(s) or terminal(s). Then go to  Step 8.
3. STEP 3. Voltage measurement at the AWD-ECU connector 
   1. Disconnect the C-57 AWD-ECU connector.
   2. Turn the ignition switch to the ON position.
   3. Measure the voltage between the C-57 wiring harness side connector terminals No. 3, No. 4 (Ignition switch "ON") and the body ground.

      OK: System voltage 

   Q: Is the check result normal? 

   1. YES:  Go to  Step 5.
   2. NO:  Go to Step 4.
4. STEP 4. Wiring harness check 

   Check the wiring harness between the C-57 AWD-ECU connector (terminal No. 4) and the C-313 ETACS-ECU connector (terminal No. 2) for damage or other problem.

   Q: Is the wiring harness in good condition? 

   1. YES:  Go to  Step 7.
   2. NO:  Repair the wiring harness. Then go to  Step 8.
5. STEP 5. Resistance measurement at the AWD-ECU connector 
   1. Disconnect the C-57 AWD-ECU connector.
   2. Measure the resistance between the C-57 wiring harness side connector terminals No. 10 and the body ground.

      OK: Continuity exists (2 Ω or less) 

   Q: Is the check result normal? 

   1. YES:  Go to  Step 7.
   2. NO:  Go to Step 6.
6. STEP 6. Wiring harness check 

   Check the wiring harness between the C-57 AWD-ECU connector (terminal No. 10) and the body ground for damage or other problem.

   Q: Is the wiring harness in good condition? 

   1. YES:  Go to Step 7.
   2. NO:  Repair the wiring harness. Then go to  Step 8.
7. STEP 7. Retest the system. 

   Q: Does the malfunction occur again? 

   1. YES:  Replace AWD-ECU (Refer to AWD-ECU  ). Then go to Step 8.
   2. NO:  The trouble can be an intermittent malfunction (Refer to HOW TO COPE WITH INTERMITTENT MALFUNCTIONS ).
8. STEP 8. Retest the system. 

   Q: Does the malfunction occur again? 

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