Inspection Procedure 4

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

CAUTION:

- Whenever the ECU is replaced, ensure that the CAN bus lines Initial Inspection and Diagnostic Overview ) are normal.
- When the hydraulic unit (integrated with ASC-ECU) is replaced, always perform the calibration of steering wheel sensor, G and yaw rate sensor, brake fluid pressure sensor, cut valve, and inlet valve (Refer to G and Yaw Rate Sensor Calibration , Testing and Inspection , Master Cylinder Brake Fluid Pressure Sensor Calibration , and Testing and Inspection ).

CIRCUIT OPERATION

- ASC-ECU sends the illumination request signal of the brake warning light to the combination meter through ETACS-ECU via CAN communication.
- When the ignition switch is turned ON, ASC-ECU illuminates the brake warning light via ETACS-ECU for approximately 3 seconds for the purpose of bulb check.

TECHNICAL DESCRIPTION (COMMENT)

In the case of this trouble symptom, there may be a malfunction to the CAN bus line, ETACS-ECU, combination meter, or ASC-ECU.

PROBABLE CAUSES

- Damaged wiring harness and connectors
- Malfunction of ETACS-ECU
- Combination meter malfunction
- ASC-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 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 CAN Bus Diagnostics Chart).
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 Active Stability Control System (ASC)).
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 Actuator Test Reference Table).

- Item 07: Indicator1

Q. Is the check result normal?

YES Go to Step 4.
NO Carry out the diagnosis of the combination meter Symptom Chart). Then go to Step 7.
STEP 4. Scan tool diagnostic trouble code for other system

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 Combination Meter).
Then go to Step 7.
NO Go to Step 5.
STEP 5. Scan tool diagnostic trouble code for other system

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 Electronic Time and Alarm Control System (ETACS).
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 How to Cope With Intermittent Malfunctions).
NO Replace the hydraulic unit (integrated with ASC-ECU) (Refer to Service and Repair).
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.