Inspection Procedure 12: ASC-ECU Power Supply Circuit System

Inspection Procedure 12: ASC-ECU Power Supply Circuit 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. 4) for ASC-ECU. When the ignition switch (IG1) is turned ON, the power is supplied to the relay in ETACS-ECU, and the relay turns ON. Then, the power is sent to ASC-ECU from the fusible link No. 34 through the multi-purpose fuse No. 12.
^ When malfunction occurs in 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 PROCEDURE

STEP 1. Battery check
Refer to 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
Refer to Charging System.
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-02 ASC-ECU connector
Q: Is the check result normal?
YES: Go to Step 4.
NO: Repair the damaged connector.

STEP 4. Fusible link check: Check the fusible link No.27.
Q: Is the check result normal?
YES: Go to Step 6.
NO: Go to Step 5.

STEP 5. Resistance measurement at A-02 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) 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.
NO: Repair the harness between the fusible link No.27 and A-02 ASC-ECU connector terminal No.32. Then replace the fusible link No.27.

STEP 6. Check the fuse No.12.
Visually check for open circuit in the fuse No.12.
Q: Is the check result normal?
YES: Go to Step 9.
NO: Go to Step 7.

STEP 7. Connector check: C-33 intermediate connector, C-317 ETACS-ECU connector
Q: Is the check result normal?
YES: Go to Step 8.
NO: Repair the defective connector.

STEP 8. Resistance measurement at A-02 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) Resistance between the terminal No.4 and the body ground.
OK: No continuity
Q: Is the check result normal?
YES: Replace the fuse No.12. Then go to Step 11.
NO: Repair the harness between the C-317 ETACS-ECU connector terminal No.5 and A-02 ASC-ECU connector terminal No.4. Then replace the fuse No.12.

STEP 9. Connector check: C-317 ETACS-ECU connector
Q: Is the check result normal?
YES: Go to Step 10.
NO: Repair the damaged connector.

STEP 10. Resistance measurement at C-309 ETACS-ECU connector
1) Removal the fusible link No.34.
2) Disconnect the C-309 ETACS-ECU connector, and then measure the resistance at the connector side.
3) 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.34.
NO: Repair the harness between the fusible link No.33 and C-309 ETACS-ECU connector terminal No.1. Then replace the fusible link No.34.

STEP 11. Voltage measurement at the A-02 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 battery voltage
Q: Is the check result normal?
YES: Go to Step 12.
NO: Repair the wiring harness between A-02 ASC-ECU connector terminal No.32 and fusible link No.27.

STEP 12. Connector check: C-309 ETACS-ECU connector
Q: Is the check result normal?
YES: Go to Step 13.
NO: Repair the damaged connector.

STEP 13. Voltage measurement at the C-309 ETACS-ECU connector.
1) Disconnect the connector, and measure at the wiring harness-side connector.
2) Voltage between the terminal No.1 and the body ground
OK: Approximately battery voltage
Q: Is the check result normal?
YES: Go to Step 14.
NO: Repair the wiring harness between C-309 ETACS-ECU connector terminal No.1 and fusible link No.33.

STEP 14. Connector check: C-317 ETACS-ECU connector
Q: Is the check result normal?
YES: Go to Step 15.
NO: Repair the defective connector.

STEP 15. Voltage measurement at the C-317 ETACS-ECU connector
1) Measure by backprobing without disconnecting the connector.
2) Turn the ignition switch to the ON position.
3) Voltage between the terminal No.6 and the body ground
OK: Approximately battery voltage
Q: Is the check result normal?
YES: Go to Step 17.
NO: Go to Step 16.

STEP 16. Connector check: C-210 ignition switch connector
Q: Is the check result normal?
YES: Repair the wiring harness between C-210 ignition switch connector terminal No.2 and C-317 ETACS-ECU connector terminal No.6.
NO: Repair the damaged connector.

STEP 17. Connector check: C-317 ETACS-ECU connector
1) Measure at ETACS-ECU side connector.

NOTE: Do not disconnect the connector.

2) Turn the ignition switch to the ON position.
3) Measure the voltage between terminal No.5 and the body ground by backprobing.
OK: Approximately battery voltage
Q: Is the check result normal?
YES: Go to Step 18.
NO: Replace the ETACS-ECU. Then go to Step 22.

STEP 18. Connector check: C-33 intermediate connector
Q: Is the check result normal?
YES: Go to Step 19.
NO: Repair the defective connector.

STEP 19. Voltage measurement at the A-02 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) 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 21.
NO: Repair the wiring harness.

STEP 21. Retest the system.
Q: Is the communication with M.U.T.-III possible?
YES: Intermittent malfunction.
NO: Make sure that the M.U.T.-III cable is properly connected and the V.C.I. switch is ON, and then replace the ASC-ECU. Then go to Step 22.

STEP 22. Retest the system.
Q: Is the communication with M.U.T.-III possible?
YES: Return to Step 1.
NO: This diagnosis is complete.