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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 (Refer to GROUP 54C - CAN Bus Line Diagnostic 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 , and ).
 
 
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
STEP 1. Using scan tool MB991958, diagnose the CAN bus lines.
Use scan tool to diagnose the CAN bus lines.
Is the check result normal?
Go to Step 2.
Repair the CAN bus lines (Refer to GROUP 54C - CAN Bus Diagnostics Table ). 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.
Is the DTC set?
Carry out the diagnosis for the DTC (Refer to ).
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 (Refer to GROUP 54A - Combination Meter/Actuator Test Table , ).
  • Item No.07: Indicator 1
Is the check result normal?
Go to Step 4.
Diagnose the combination meter (Refer to GROUP 54A - Combination Meter/Trouble 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.
Is the DTC set?
Diagnose the combination meter (Refer to GROUP 54A - Combination Meter/DTC ). Then go to Step 7.
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.
Is the DTC set?
Perform troubleshooting on ETACS-ECU (Refer to GROUP 54A - ETACS/DTC ). Then go to Step 7.
Go to Step 6.
 
STEP 6. Retest the system.
Does the brake warning light turn ON and OFF
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/How to Cope with Intermittent Malfunctions ).
Replace the hydraulic unit (integrated with ASC-ECU) (Refer to ), and then go to Step 7.
 
STEP 7. Retest the system.
Does the brake warning light turn ON and OFF normally?
The procedure is complete.
Return to Step 1.