Inspection Procedure 1: Scan tool MB991958 cannot Communicate with the Electronic Control AWD System: Diagnosis

WARNING: This page is about a different variant/trim than selected.

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

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 TROUBLESHOOTING/CAN BUS DIAGNOSTICS TABLE . On completion, go to Step 2.
STEP 2. Check the following connector:
Check the connectors below for improper engagement, terminal damage or terminal drawn in the connector case.
- C-128 AWD-ECU connector
- C-309, C-313 ETACS-ECU connector
- C-138 intermediate connector
  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.
STEP 3. Voltage measurement at the AWD-ECU connector
1. Disconnect the C-128 AWD-ECU connector.
2. Turn the ignition switch to the ON position.
3. Measure the voltage between the C-128 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.
STEP 4. Wiring harness check
Check the wiring harness between the C-128 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.
STEP 5. Resistance measurement at the AWD-ECU connector
1. Disconnect the C-128 AWD-ECU connector.
2. Measure the resistance between the C-128 wiring harness side connector terminals No. 10 and the body ground.
  OK: Continuity exists (2 ohm or less)
  
  Q: Is the check result normal?
  1. YES: Go to Step 7.
  2. NO: Go to Step 6.
STEP 6. Wiring harness check
Check the wiring harness between the C-128 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.
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 .
STEP 8. Retest the system.
Q: Does the malfunction occur again?
1. YES: Diagnose again from Step 1.
2. NO: The procedure is complete.