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.

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

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.
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.
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.
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.
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.
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.
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.