Inspection Procedure 11

Inspection Procedure 11: ASC-ECU power supply circuit system

CAUTION:

- When the ASC-ECU power supply voltage becomes 9.7± 0.3 V or less, the ABS warning light, ASC warning display, and ASC OFF display illuminate, and the ABS, stability control, and TCL controls are prohibited.
- If the battery terminal is not tightened properly, a dump surge may occur and the power supply voltage may become abnormally high for a short period of time.
- 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 Initial Inspection and Diagnostic Overview ).
- Whenever the ECU is replaced, ensure that the CAN bus lines 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 ).

SYSTEM OPERATION

- ASC-ECU contains the power supply circuit (terminal No. 32) for the solenoid valve. The solenoid valve is energized by the valve relay, which is incorporated in ASC-ECU.
- ASC-ECU contains the power supply circuit (terminal No. 1) for the pump motor. The pump motor is energized by the motor relay, which is incorporated in ASC-ECU.
- ASC-ECU contains the power supply circuit (terminal No. 2) for ASC-ECU, and the power is supplied from the fusible link No. 34 through the multi-purpose fuse No. 17.
- If a malfunction occurs in the ASC-ECU power supply, the communication with scan tool becomes unavailable.

PROBABLE CAUSES

- Damaged wiring harness and connectors
- Malfunction of fuse or fusible link
- Improper tightening of battery terminal
- Improper tightening of grounding bolt
- Battery failure
- Charging system failed
- 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
- MB991997: ASC check harness

STEP 1. Battery check

Battery Test.

Q. Is the battery in good condition?

YES Go to Step 3.
NO Charge or replace the battery. Then, go to Step 2.
STEP 2. Charging system check

Output Current Test.

Q. Is the charging system in good condition?

YES Go to Step 3.
NO Repair or replace the charging system component(s).
STEP 3. Connector check: A-05 ASC-ECU connector

Q. Is the check result normal?

YES Go to Step 4.
NO : Repair the defective connector.
STEP 4. Voltage measurement at A-05 ASC-ECU connector

(1)Disconnect the connector, connect the ASC check harness (Special tool: MB991997) to the wiring harness-side connector, and measure the voltage at the special tool connector side.
NOTE:
Do not connect the special tool to ASC-ECU.

(2)Measure the voltage between the terminal No. 1 and the body ground.
OK: Approximately system voltage

Q. Is the check result normal?

YES Go to Step 10.

NO Go to Step 8.

STEP 8. Fusible link check: Check the fusible link No.26.

Visually check for open circuit in the fusible link No.26.

Q. Is the check result normal?

YES An open circuit may be present in the pump motor power supply circuit. Repair the wiring harness between A-05 ASC-ECU connector terminal No. 1 and the fusible link No. 26.
NO Go to Step 9.
STEP 9. Wiring harness check between A-05 ASC-ECU connector and fusible link No. 26.

(1)Disconnect ASC-ECU connector A-05.

(2)Remove fusible link No. 26.

(3)Check the continuity (short to ground) between A-05 ASC-ECU connector terminal No. 1 and the ground.
OK: No continuity

Q. Is the check result normal?

YES Replace the fusible link No.26.
NO Short circuit may be present in the power supply circuit. Repair the wiring harness between A-05 ASC-ECU connector terminal No. 1 and fusible link No. 26.
STEP 10. Check of fuse No. 17 and fusible link No. 34

Visually check for open circuit in the fuse No. 17 and the fusible link No. 34.

Q. Is the check result normal?

YES Go to Step 14.
NO Go to Step 11.
STEP 11. Connector check: C-42 intermediate connector, C-46 ETACS-ECU connector, C-131 intermediate connector, C-309 ETACS-ECU connector and C-315 ETACS-ECU connector

Q. Is the check result normal?

YES Go to Step 12.
NO Repair the connector. Then, replace fuse No. 17 or fusible link No. 34.
STEP 12. Wiring harness check between C-309 ETACS-ECU connector and fusible link No. 34.

(1)Remove fusible link No. 34.

(2)Disconnect ETACS-ECU connector C-309, and measure at the wiring harness side.

(3)Check the continuity (short to ground) between terminal No. 1 and the ground.
OK: No continuity

Q. Is the check result normal?

YES Go to Step 13.
NO Repair the wiring harness between C-309 ETACS-ECU connector terminal No. 1 and fusible link No. 34. Then, replace fuse No. 17 or fusible link No. 34.
STEP 13. Wiring harness check.

(1)Disconnect the C-315 ETACS-ECU connector.

(2)Disconnect the C-46 AWC-ECU connector.

(3)Disconnect the A-05 ASC-ECU, and measure at the wiring harness side.

(4)Check the continuity (short to ground) between terminal No.17 and the ground.
OK: No continuity

Q. Is the check result normal?

YES Replace the fuse No. 17 or the fusible link No. 34. Then, go to Step 18.
NO Repair the wiring harness. Then, replace fuse No. 17 or fusible link No. 34.
STEP 14. Voltage measurement at A-05 ASC-ECU connector