Inspection Procedure 4: ABS Warning Light Does Not Illuminate When Ignition Switch Is Turned to the ON Position (Engine Stopped

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

CAUTION:
^ If there is any problem in the CAN bus lines, an incorrect diagnostic trouble code may be set. Prior to this diagnosis, diagnose the CAN bus lines.
^ Before replacing the ECU, ensure that the communication circuit is 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.

OPERATION
^ ASC-ECU sends the illumination request signal of the ABS warning light to the combination meter through ETACS-ECU via CAN communication.
^ ASC-ECU illuminates the ABS warning light via ETACS-ECU for approximately 3 seconds for valve 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
^ Combination meter malfunction
^ ASC-ECU malfunction
^ The ETACS-ECU coding data is abnormal.

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

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 ASC system.
Q: Is the DTC set?
YES: Carry out the diagnosis for the diagnostic trouble code.
NO: Go to Step 3.

STEP 3. M.U.T.-III actuator test
Perform the actuator test No.07 of the combination meter system, and check if the ABS warning light illuminates.
Q: Is the check result normal?
YES: Go to Step 4.
NO: Troubleshoot the combination meter, and then go to Step 7.

STEP 4. ETACS-ECU coding data check
Q: Is the check result normal?
YES: Go to Step 5.
NO: Replace the ETACS-ECU, and then go to Step 7.

STEP 5. M.U.T.-III other system diagnostic trouble code
Using M.U.T.-III, check that DTC U0141 is not set by the combination meter system.
Q: Is the DTC U0141 set?
YES: Troubleshoot the combination meter, and then go to Step 7.
NO: Go to Step 6.

STEP 6. M.U.T.-III other system diagnostic trouble code
Using M.U.T.-III, check that DTC U0121 is not set by the ETACS system.
Q: Is the DTC U0121 set?
YES: Troubleshoot the ETACS-ECU, and then go to Step 7.
NO: Replace the ASC-ECU. Then go to Step 7.

STEP 7. Retest the system.
Q: Does the ABS warning light turn ON and OFF normally?
YES: This diagnosis is complete.
NO: Return to Step 1.