Inspection Procedure 4: Brake Warning Light Does Not Illuminate When the Ignition Switch Is Turned to ON Position

Inspection Procedure 4: Brake Warning Light does not Illuminate when the Ignition Switch is Turned to ON Position (Engine Stopped).

CIRCUIT OPERATION
ABS-ECU sends the illumination request signal of the brake warning light to the combination meter through ETACS-ECU via the CAN communication.

TECHNICAL DESCRIPTION (COMMENT)
This may be caused by faults in the CAN bus line, ETACS-ECU, combination meter or ABS-ECU.

PROBABLE CAUSES
^ Damaged wiring harness and connectors
^ Malfunction of ETACS-ECU
^ Combination meter malfunction
^ ABS-ECU malfunction

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. M.U.T.-III CAN bus diagnostics
Use scan tool to diagnose the CAN bus lines.
Q: Is the check result normal?
YES: Go to Step 2.
NO: Repair the CAN bus lines.

STEP 2. M.U.T.-III diagnostic trouble code
Use scan tool to check the diagnostic trouble code for the ABS system.
Q: Is the diagnostic trouble code set?
YES: Carry out the diagnosis for the diagnostic trouble code.
NO: Go to Step 3.

STEP 3. M.U.T.-III other system diagnostic trouble code
Using scan tool, check that the diagnostic trouble code No. U0141 is not set by the combination meter system.
Q: Is the diagnostic trouble code set?
YES: Troubleshoot the combination meter, then go to Step 5.
NO: Go to Step 4.

STEP 4. M.U.T.-III other system diagnostic trouble code
Using scan tool, check that the diagnostic trouble code No. U0121 is not set by the ETACS system.
Q: Is the diagnostic trouble code set?
YES: Troubleshoot the ETACS, then go to Step 5.
NO: Replace the ABS-ECU, then go to Step 5.

STEP 5. Retest the system.
Q: Does the brake warning light turn ON and OFF normally?
YES: The procedure is complete.
NO: Return to Step 1.