Inspection Procedure 12

Inspection Procedure 12: ASC-ECU Power Supply Circuit System

Solenoid Valve, Motor and ASC-ECU Power Supply Circuit:

SYSTEM OPERATION
^ The ASC-ECU power supply signal energized by the ignition switch (IG1) is transmitted to ASC-ECU (terminal No. 4) via the multi-purpose fuse No.12.
^ The ASC-ECU power supply and the valve power supply are transmitted to ASC-ECU (terminal No. 32) via the fusible link No. 27.
^ When malfunction occurs in ASC-ECU power supply, the communication with scan tool becomes unavailable.

PROBABLE CAUSES
^ Damaged wiring harness and connectors
^ 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. Voltage measurement at the A-02 ASC-ECU connector

(1) Disconnect the connector, connect special tool MB991997 to the harness-side connector, and measure the voltage at the special tool connector side.

NOTE: Do not connect the special tool MB991997 to ASC-ECU.

(2) Turn the ignition switch to the ON position.
(3) Voltage between the terminal No. 1 and the body ground
OK: 12 volts (Battery voltage)
Q: Is the check result normal?
YES: Go to Step 7.
NO: Go to Step 5.

STEP 5. Connector check: A-02 ASC-ECU connector
Q: Is the check result normal?
YES: Repair the wiring harness between the fusible link No. 26 and the A-02 ASC-ECU connector terminal No. 1.
NO: Repair the defective connector.

STEP 6. Connector check: A-02 ASC-ECU connector, C-33 intermediate connector, C-317 junction block connector, C-210 ignition switch connector
Q: Is the check result normal?
YES: The open or short circuit may be present in the power supply circuit. Repair the wiring harness between the A-02 ASC-ECU connector terminal No. 4 and the C-210 ignition switch connector.
NO: Repair the defective connector.

STEP 7. Wiring harness check between the A-02 ASC-ECU connector terminal No. 16/47 and the body ground
^ Check the ground wires for open circuit.

Q: Is the check result normal?
YES: Go to Step 8.
NO: Repair the wiring harness.

STEP 8. Battery check
Q: Is the battery in good condition?
YES: Go to Step 9.
NO: Charge or replace the battery.

STEP 9. Charging system check
Q: Is the charging system in good condition?
YES: Go to Step 10.
NO: Repair or replace the charging system component(s).

STEP 10. Retest the system.
Q: Is the communication with scan tool possible?
YES: An intermittent malfunction may be present.
NO: Make sure that the M.U.T.-III cable is properly connected and the V.C.I. switch is ON, and then replace ASC-ECU.