Inspection Procedure 12

Inspection Procedure 12: 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 lamp, 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 time.

- 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 Testing and Inspection, Testing and Inspection and Testing and Inspection).

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.2) for ASC-ECU. The power is supplied from the fusible link No.34 through the multi-purpose fuse No.17.

- ASC-ECU contains the power supply circuit (terminal No.8) for ASC-ECU. When the ignition switch (IG1) is turned ON, the voltage is applied to the relay incorporated in ETACS-ECU to turn ON the relay, and the power is supplied from the fusible link No.34 through multi-purpose fuse No.12.

- ASC-ECU contains the power supply circuit (terminal No.1) for the pump motor. The pump motor is energized by the motor switch, which is incorporated in ASC-ECU.

- When malfunction occurs in ASC-ECU power supply, the communication with scan tool becomes unavailable.

PROBABLE CAUSES

- Damaged wiring harness and connectors

- Fuse and fusible link malfunction

- Improper tightening of battery terminal

- Improper tightening of ground 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

Generator Output Line Voltage Drop 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-51 ASC-ECU connector, C-128 intermediate connector, C-317 ETACS-ECU connector, C-315 ETACS-ECU connector

Q. Is the check result normal?

YES Go to Step 4.
NO : Repair the damaged connector.
STEP 4. Voltage measurement at the A-51 ASC-ECU connector





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

(2)Measure the voltage between terminal No.32 and body ground.
OK: Approximately system voltage

Q. Is the check result normal?

YES Go to Step 7.

NO Go to Step 5.

STEP 5. Fusible link check: Check the fusible link No.27.

Q. Is the check result normal?

YES The open circuit may be present in the power supply circuit. Repair the wiring harness between the A-51 ASC-ECU connector terminal No.32 and the fusible link No.27. Then go to Step 20.
NO Go to Step 6.
STEP 6. Resistance measurement at A-51 ASC-ECU connector





(1)Removal the fusible link No.27.
(2)Disconnect the ASC-ECU connector, connect special tool ASC check harness (MB991997) to the harness-side connector, and then measure the resistance at the special tool connector side.
NOTE:
Do not connect the special tool ASC check harness (MB991997) to ASC-ECU.

(3)Measure the resistance between the terminal No.32 and the body ground.
OK: No continuity

Q. Is the check result normal?

YES Replace the fusible link No.27. Then go to Step 20.

NO The short circuit may be present in the power supply circuit. Repair the wiring harness between the A-51 ASC-ECU connector terminal No.32 and the fusible link No.27, and then replace the fusible link No.27. Then go to Step 20.

STEP 7. Voltage measurement at the A-51 ASC-ECU connector





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

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

Q. Is the check result normal?

YES Go to Step 10.

NO Go to Step 8.

STEP 8. Check the fusible link No.26.

Q. Is the check result normal?

YES The open circuit may be present in the power supply circuit. Repair the wiring harness between the A-51 ASC-ECU connector terminal No.1 and the fusible link No.26. Then go to Step 20.
NO Go to Step 9.
STEP 9. Resistance measurement at A-51 ASC-ECU connector

(1)Removal the fusible link No.26.





(2)Disconnect the ASC-ECU connector, connect special tool ASC check harness (MB991997) to the harness-side connector, and then measure the resistance at the special tool connector side.
NOTE:
Do not connect the special tool ASC check harness (MB991997) to ASC-ECU.

(3)Measure the resistance between the terminal No.1 and the body ground.
OK: No continuity

Q. Is the check result normal?

YES Replace the fusible link No.26. Then go to Step 20.

NO The short circuit may be present in the power supply circuit. Repair the wiring harness between the A-51 ASC-ECU connector terminal No.1 and the fusible link No.26, and then replace the fusible link No.26. Then go to Step 20.

STEP 10. Voltage measurement at the A-51 ASC-ECU connector





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

(2)Ignition switch: ON position.
(3)Measure the voltage between terminal No.8 and body ground.
OK: Approximately system voltage

Q. Is the check result normal?

YES Go to Step 14.

NO Go to Step 11.

STEP 11. Check the fuse No.12.

Visually check for open circuit in fuse No.12.

Q. Is the check result normal?

YES Go to Step 12.
NO Go to Step 13.
STEP 12. Resistance measurement at A-51 ASC-ECU connector

(1)Disconnect the C-317 ETACS-ECU connector.





(2)Disconnect the A-51 ASC-ECU connector, connect special tool ASC check harness (MB991997) to the harness-side connector, and then measure the resistance at the special tool connector side.
NOTE:
Do not connect the special tool ASC check harness (MB991997) to ASC-ECU.

(3)Measure the resistance between the A-51 ASC-ECU connector terminal No.8 and the C-317 ETACS-ECU connector terminal No.5.
OK: Continuity exists (2 ohms or less)

Q. Is the check result normal?

YES The trouble can be an intermittent malfunction How to Cope With Intermittent Malfunctions).

NO The open circuit may be present in the power supply circuit. Repair the wiring harness between the A-51 ASC-ECU connector terminal No.8 and the C-317 ETACS-ECU connector terminal No.5. Then go to Step 20.

STEP 13. Resistance measurement at A-51 ASC-ECU connector





(1)Disconnect the C-317 ETACS-ECU connector.
(2)Disconnect the ASC-ECU connector, connect special tool ASC check harness (MB991997) to the harness-side connector, and then measure the resistance at the special tool connector side.
NOTE:
Do not connect the special tool ASC check harness (MB991997) to ASC-ECU.

(3)Measure the resistance between the terminal No.8 and the body ground.
OK: No continuity

Q. Is the check result normal?

YES Replace the fuse No.12. Then go to Step 20.

NO The short circuit may be present in the power supply circuit. Repair the wiring harness between the A-51 ASC-ECU connector terminal No.8 and the C-317 ETACS-ECU connector terminal No.5, and then replace the fuse No.12. Then go to Step 20.

STEP 14. Voltage measurement at the A-51 ASC-ECU connector





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

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

Q. Is the check result normal?

YES Go to Step 18.

NO Go to Step 15.

STEP 15. Check the fuse No.17.

Visually check for open circuit in fuse No.17.

Q. Is the check result normal?

YES Go to Step 16.
NO Go to Step 17.
STEP 16. Resistance measurement at A-51 ASC-ECU connector

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





(2)Disconnect the A-51 ASC-ECU connector, connect special tool ASC check harness (MB991997) to the harness-side connector, and then measure the resistance at the special tool connector side.
NOTE:
Do not connect the special tool ASC check harness (MB991997) to ASC-ECU.

(3)Measure the resistance between the A-51 ASC-ECU connector terminal No.2 and the C-315 ETACS-ECU connector terminal No.4.
OK: Continuity exists (2 ohms or less)

Q. Is the check result normal?

YES The trouble can be an intermittent malfunction How to Cope With Intermittent Malfunctions).

NO The open circuit may be present in the power supply circuit. Repair the wiring harness between the A-51 ASC-ECU connector terminal No.2 and the C-315 ETACS-ECU connector terminal No.4. Then go to Step 20.

STEP 17. Resistance measurement at A-51 ASC-ECU connector





(1)Disconnect the C-315 ETACS-ECU connector.
(2)Disconnect the ASC-ECU connector, connect special tool ASC check harness (MB991997) to the harness-side connector, and then measure the resistance at the special tool connector side.
NOTE:
Do not connect the special tool ASC check harness (MB991997) to ASC-ECU.

(3)Measure the resistance between the terminal No.2 and the body ground.
OK: No continuity

Q. Is the check result normal?

YES Replace the fuse No.17. Then go to Step 20.

NO The short circuit may be present in the power supply circuit. Repair the wiring harness between the A-51 ASC-ECU connector terminal No.2 and the C-315 ETACS-ECU connector terminal No.4, and then replace the fuse No.17. Then go to Step 20.

STEP 18. Resistance measurement at the A-51 ASC-ECU connector





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

(2)Measure the resistance between terminal No.16 and body ground, and between terminal No.47 and body ground.
OK: Continuity exists (2 ohms or less)

Q. Is the check result normal?

YES Go to Step 19.

NO An open circuit may be present in the ground circuit. Repair the wiring harness between the A-51 ASC-ECU connector terminal No.16 and the body ground, and between the A-51 ASC-ECU connector terminal No.47 and the body ground.

STEP 19. Retest the system.

Make sure that the scan tool cable is properly connected and the V.C.I. switch is ON.

Q. Is the communication with scan tool possible?

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)).
Then go to Step 20.
STEP 20. Retest the system.

Q. Is the communication with scan tool possible?

YES Return to Step 1.
NO This diagnosis is complete.