Inspection Procedure 6: ABS Warning Light Stays on After the Engine Is Started

Inspection Procedure 6: ABS warning light stays ON after the engine is started.

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 Trouble code diagnosis Diagnostic Trouble Code Descriptions).
^ 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.

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
^ Control stop due to the low voltage

NOTE: Due to the abnormality in the supply voltage, the DTC may not be set even when the ABS warning light is illuminated.

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. (Refer to Troubleshooting Symptom Chart.) Then go to Step 8.

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 Diagnostic Trouble Code Descriptions).
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 ABS warning light illuminates normally.
(Refer to Combination Meter, Actuator Test Table Scan Tool Testing and Procedures[Vehicles without color liquid crystal display] or [Vehicles with color liquid crystal display].)
^ Item No.07: Indicator 1
Q: Is the check result normal?
YES: Go to Step 4.
NO: Replace the combination meter. Then go to Step 8.

STEP 4. Check the ASC-ECU power supply circuit system.
Refer to Inspection Procedure 12: ASC-ECU Power Supply Circuit System.
Q: Is the check result normal?
YES: Go to Step 5.
NO: Diagnose the power supply circuit of the ASC-ECU (Refer to Inspection Procedure 12: ASC-ECU Power Supply Circuit System).

STEP 5. 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. (Refer to Combination Meter, Troubleshooting Testing and Inspection.) Then go to Step 8.
NO: Go to Step 6.

STEP 6. 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. (Refer to ETACS, Troubleshooting Diagnostic Trouble Code Descriptions.) Then go to Step 8.
NO: Go to Step 7.

STEP 7. Retest the system.
Q: Does the ABS warning light turn ON and OFF normally?
YES: Intermittent malfunction.
NO: Replace the hydraulic unit (ASC-ECU), and then go to Step 8.

STEP 8. Retest the system.
Q: Does the ABS warning light turn ON and OFF normally?
YES: The procedure is complete.
NO: Return to Step 1.