Inspection Procedure 1

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

Part 1:

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 C-128 AWD-ECU connector for improper engagement, terminal damage or terminal drawn in the connector case.
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 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

NOTE: Before the wiring harness inspection, inspect the C-313 and C-309 ETACS-ECU connectors, and repair if necessary.

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. 9 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.