Inspection Procedure 3

When the Ignition Key is Turned to "ON" (Engine Stopped), the SRS Warning Light does not Illuminate.






TECHNICAL DESCRIPTION (COMMENT)
- The SRS-ECU sends the SRS warning light signal to the combination meter via the CAN communication.
- This may be caused by faults in the CAN bus line, the combination meter or the SRS-ECU.

TROUBLESHOOTING HINTS (The most likely causes for this case:)
- Damaged wiring harness or connector
- Combination meter defect
- Malfunction of the SRS-ECU

DIAGNOSIS

Required Special Tools:
- MB991958: Scan Tool (MUT-III Sub Assembly)
- MB991824: Vehicle Communication Interface (V.C.I.)
- MB991827: MUT-III USB Cable
- MB991910: MUT-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.

Use scan tool MB991958 to diagnose the CAN bus lines.

1. Connect scan tool MB991958 to the data link connector.
2. Turn the ignition switch to the "ON" position.
3. Diagnose the CAN bus line.

Q: Is the check result satisfactory?

YES: Go to Step 2.

NO: Repair the CAN bus lines (Refer to Diagnosis-Can Bus Diagnostic Chart). Component Tests and General Diagnostics Repair the CAN bus lines, and then go to Step 2.




STEP 2. Using scan tool MB991958, read the combination meter diagnostic trouble code.

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.

Use scan tool MB991958 to check whether combination meter DTC U1112 has been set.

1. Connect scan tool MB991958 to the data link connector.
2. Turn the ignition switch to the "ON" position.
3. Check whether combination meter DTC U1112 has been set.

Q: Is combination meter DTC U1112 set?

YES: Replace the SRS-ECU.

NO: Replace the combination meter.