Inspection Procedure 4: The brake warning light does not illuminate when ignition switch is turned to the ON position (engine stopped): 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 lines.
Using scan tool MB991958, diagnose the CAN bus lines.
Q: Is the check result normal?
YES : Go to Step 2.
NO : Repair the CAN bus lines. (Refer to TROUBLESHOOTING .) Then go to Step 7.
- STEP 2. Scan tool diagnostic trouble code
Using scan tool, check the diagnostic trouble code for ASC system.
Q: Is any DTC set?
YES : Carry out the diagnosis for the DTC. (Refer to DIAGNOSTIC TROUBLE CODE CHART .)
NO : Go to Step 3.
- STEP 3. M.U.T.-III actuator test
Perform the following actuator tests from the combination meter system to check if the brake warning light is illuminated. (Refer to ACTUATOR TEST TABLE .)
- Item 07: Indicator1
Q: Is the check result normal?
YES : Go to Step 4.
NO : Carry out the diagnosis of the combination meter. (Refer to TROUBLE SYMPTOM CHART .) Then go to Step 7.
- STEP 4. Scan tool diagnostic trouble code for other systems
Using scan tool MB991958, check if diagnostic trouble code No. U0141 is set by the combination meter system.
Q: Is the DTC set?
YES : Diagnose the combination meter. (Refer to TROUBLESHOOTING .) Then go to Step 7.
NO : Go to Step 5.
- STEP 5. Scan tool diagnostic trouble code for other systems
Using scan tool MB991958, check if diagnostic trouble code No. U0121 is set by ETACS system.
Q: Is the DTC set?
YES : Diagnose the ETACS-ECU. (Refer to TROUBLESHOOTING .) Then go to Step 7.
NO : Go to Step 6.
- STEP 6. Retest the system.
Q: Does the brake warning light turn ON and OFF normally?
YES : Intermittent malfunction. (Refer to HOW TO COPE WITH INTERMITTENT MALFUNCTION .)
NO : Replace the hydraulic unit (incorporates in ASC-ECU).(Refer to HYDRAULIC UNIT .) Then go to Step 7.
- STEP 7. Retest the system.
Q: Does the brake warning light turn ON and OFF normally?
YES : The procedure is complete.
NO : Return to Step 1.