Inspection Procedure 1
SYMPTOM PROCEDURESInspection Procedure 1: Scan tool MB991958 cannot Communicate with the Electronic Control AWD System.
COMMENTS ON TROUBLE SYMPTOM
If scan tool MB991958 cannot communicate with the electronic control AWD system, the CAN bus lines may have a problem. If the electronic control AWD system is not in operation (in case of no AWD operation), the AWD-ECU power supply circuit system or AWD-ECU may have a problem.
TROUBLESHOOTING HINTS
^ Damaged wiring harness and connectors
^ AWD-ECU malfunction
DIAGNOSIS
^ 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?
YES: Go to Step 2.
NO: Repair the CAN bus line. 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
Q:Are the connectors and terminals in good condition?
YES: Go to Step 3.
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.4 (Ignition switch "ON") and the body earth.
OK: Battery voltage
Q:Is the check result normal?
YES: Go to Step 5.
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-309 ETACS-ECU connector (terminal No.1) for damage or other problem.
Q:Is the wiring harness in good condition?
YES: Go to Step 7.
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 earth.
OK: 2 ohm or less
Q:Is the check result normal?
YES: Go to Step 7.
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 earth (No.10 or No.18) for damage or other problem.
Q:Is the wiring harness in good condition?
YES: Go to Step 7.
NO: Repair the wiring harness. Then go to Step 8.
STEP 7. Retest the system.
Q:Does the malfunction occur again?
YES: Replace AWD-ECU. Then go to Step 8.
NO: The trouble can be an intermittent malfunction.
STEP 8. Check whether the DTC is reset.
Q:Does the malfunction occur again?
YES: Diagnose again from Step 1.
NO: This diagnosis is complete.