Inspection Procedure 5

Inspection Procedure 5: 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 Line Diagnostics Flow ).
- Whenever ECU is replaced, ensure that the CAN bus lines are normal.
- When the hydraulic unit (integrated with ASC-ECU) is replaced, always carry out the calibration of the steering wheel sensor, the G and yaw rate sensor and brake fluid pressure sensor (Refer to Active Stability Control System (ASC) , Active Stability Control System (ASC) and Active Stability Control System (ASC) ).

OPERATION

- ASC-ECU sends the illumination request signal of the break warning light to the combination meter through ETACS-ECU via the CAN communication.
- ASC-ECU illuminates brake warning light 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 ASC-ECU.

PROBABLE CAUSES

- Damaged wiring harness and connectors
- Malfunction of ETACS-ECU
- Malfunction of the combination meter
- 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.

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.) Then go to Step 7.
STEP 2. Using scan tool MB991958, check the DTC

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

Q. Is the DTC set?

YES Carry out the diagnosis for the DTC (Refer to Active Stability Control System (ASC)).
NO Go to Step 3.
STEP 3. Actuator test of combination meter

Perform the following actuator test by the combination meter system, and check if the brake warning light illuminates Actuator Test Table [Vehicles Without Color Liquid Crystal Display]).

- Item No.07: Indicator 1

Q. Is the check result normal?

YES Go to Step 4.
NO Diagnose the combination meter Symptom Chart). Then go to Step 7.
STEP 4. Using scan tool MB991958, check the other system DTC

Using scan tool, check that DTC U0141 is not 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. Using scan tool MB991958, check the other system DTC

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

Q. Is the DTC set?

YES Perform troubleshooting on 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

YES Intermittent malfunction How to Cope With Intermittent Malfunctions).
NO Replace the hydraulic unit (integrated with ASC-ECU) (Refer to Active Stability Control System (ASC)), and 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.