Inspection Procedure 4

Inspection Procedure 4: Brake warning light does not illuminate when the ignition switch is turned to ON position
(engine stopped).

CAUTION:

- If there is any problem in the CAN bus lines, an incorrect DTC may be set. Prior to this diagnosis, diagnose the CAN bus lines CAN Bus Diagnostics Chart).

- Whenever ECU is replaced, ensure that the CAN bus lines are normal.

CIRCUIT OPERATION

- ABS-ECU sends the illumination request signal of the break warning lamp to the combination meter through ETACS-ECU via the CAN communication.

- ABS-ECU illuminates brake warning lamp via ETACS-ECU for approximately 3 seconds for bulb check with the ignition switch turned to the ON position.

COMMENTS ON TROUBLE SYMPTOM

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

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 CAN Bus Diagnostics Chart).
STEP 2. Scan tool DTC

Use scan tool to check the DTC for the ABS system.

Q. Is the DTC set?

YES Carry out the diagnosis for the DTC (Refer to Anti-Lock Braking System (ABS)).
NO Go to Step 3.
STEP 3. Scan tool other system DTC

Using scan tool, check that the DTC U0141 is not set by the combination meter system.

Q. Is the DTC set?

YES Troubleshoot the combination meter Symptom Chart), and then go to Step 5.
NO Go to Step 4.
STEP 4. Scan tool other system DTC

Using scan tool, check that the DTC U0121 is not set by the ETACS system.

Q. Is the DTC set?

YES Troubleshoot the ETACS Electronic Time and Alarm Control System (ETACS)), and then go to Step 5.
NO Replace the hydraulic unit (integrated with ABS-ECU) (Refer to Anti-Lock Braking System (ABS)), and 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.