Inspection Procedure 13: ASC-ECU Power Supply Circuit System




















caution If there is any problem in the CAN bus lines, an incorrect diagnosis code may be set. Prior to this diagnosis, diagnose the CAN bus lines (Refer to GROUP 54C, Trouble code diagnosis ).

OPERATION

  • The ASC-ECU power supply signal energised 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 M.U.T.-III becomes unavailable.

PROBABLE CAUSES

  • Damaged wiring harness and connectors
  • Battery failure
  • Charging system failed
  • ASC-ECU malfunction

DIAGNOSIS PROCEDURE

STEP 1. Voltage measurement at the A-03 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)Turn the ignition switch to the ON position.
(3)Measure the voltage between terminal No. 4 and body earth.
OK: Approximately battery voltage

Q. Is the check result normal?

Go to Step 2.

Go to Step 6.

STEP 2. Voltage measurement at the A-03 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)Turn the ignition switch to the ON position.
(3)Measure the voltage between the terminal No. 32 and the body earth.
OK: Approximately battery voltage

Q. Is the check result normal?

Go to Step 4.

Go to Step 3.

STEP 3. Connector check: A-03 ASC-ECU connector

Q. Is the check result normal?
Repair the wiring harness between the fusible link No. 27 and the A-03 ASC-ECU connector terminal No. 32.
Repair the defective connector.

STEP 4. Voltage measurement at the A-03 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)Turn the ignition switch to the ON position.
(3)Voltage between the terminal No. 1 and the body earth
OK: Approximately battery voltage

Q. Is the check result normal?

Go to Step 7.

Go to Step 5.

STEP 5. Connector check: A-03 ASC-ECU connector

Q. Is the check result normal?
Repair the wiring harness between the fusible link No. 26 and the A-03 ASC-ECU connector terminal No. 1.
Repair the defective connector.

STEP 6. Connector check: A-03 ASC-ECU connector, C-37 intermediate connector, C-317 junction block connector, C-208 ignition switch connector

Q. Is the check result normal?
The open or short circuit may be present in the power supply circuit. Repair the wiring harness between the A-03 ASC-ECU connector terminal No. 4 and the C-208 ignition switch connector.
Repair the defective connector.

STEP 7. Wiring harness check between the A-03 ASC-ECU connector terminal No. 16/47 and the body earth

  • Check the earth wires for open circuit.

Q. Is the check result normal?
Go to Step 8.
Repair the wiring harness.

STEP 8. Battery check
Refer to GROUP 54A - Battery Test .

Q. Is the battery in good condition?
Go to Step 9.
Charge or replace the battery.

STEP 9. Charging system check
Refer to GROUP 16 - Charging System .

Q. Is the charging system in good condition?
Go to Step 10.
Repair or replace the charging system component(s).

STEP 10. Retest the system.

Q. Is the communication with M.U.T.-III possible?
Intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent Malfunction ).
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.