Inspection Procedure 1

Inspection Procedure 1: Scan tool cannot communicate with WCM.

CAUTION: Before replacing the ECU, ensure that the communication circuit is normal.

TECHNICAL DESCRIPTION (COMMENT)
WCM communicates with scan tool via CAN. Therefore, communication error of WCM is suspected.

TROUBLESHOOTING HINTS
- Malfunction of the power supply or ground of WCM.
- Malfunction of CAN bus line.

DIAGNOSIS

Required Special Tools:
MB991958: Scan Tool (M.U.T.-III Sub Assembly)
MB991824: Vehicle Communication Interface (V.C.I.)
MB991827: M.U.T.-III USB Cable
MB991910: M.U.T.-III Main Harness A (Vehicles with CAN communication system)

STEP 1. Using scan tool MB991958, diagnose the CAN bus line.






CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.

1. Connect scan tool MB991958. Refer to "How to connect the Scan Tool (M.U.T.-III)." How to Connect the Scan Tool (M.U.T.-III)
2. Turn the ignition switch to the "ON" position.
3. Diagnose the CAN bus line.
4. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the CAN bus line found to be normal?

YES : Go to Step 2.

NO : Repair the CAN bus line.

STEP 2. Check the power supply circuit and the ground circuit to WCM.
Refer to INSPECTION PROCEDURE 4 "Check WCM Power Supply/Ground Circuits". Inspection Procedure 4

Q: Is the power supply circuit and the ground circuit to WCM in good condition?

YES : Go to Step 3.

NO : Repair the power supply circuit and the ground circuit to WCM.

STEP 3. Retest the system
Check if scan tool can communicate with WCM.

Q: Does the scan tool cannot communicate with WCM in good condition?

YES : The trouble can be an intermittent malfunction (Refer to General (Body and Chassis) - How to use Troubleshooting/ inspection Service Points - How to Cope with Intermittent Malfunction).

NO : Replace WCM and register the ID codes.