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)

If the scan tool cannot communicate with the WCM, the CAN bus lines may be defective.
If the WCM does not work, the WCM or the power supply circuit may be defective.

TROUBLESHOOTING HINTS

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

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

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





(1)
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.

Connect scan tool MB991958. Refer to "How to connect the Scan Tool (M.U.T.-III) Reading and Clearing Diagnostic Trouble Codes".
(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 CAN Bus Diagnostics Chart).

STEP 2. Check the power supply circuit and the ground circuit to WCM.

Refer to Inspection Procedure 4 "Abnormality in WCM power supply and 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 communicate with WCM?

YES The trouble can be an intermittent malfunction How to Cope With Intermittent Malfunctions).
NO Replace WCM and register the ID codes (Refer to ID registration procedure manual - ID codes registration judgement table).