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 ).
  • 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 , and ).

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.
  • The ASC-ECU power supply and the valve power supply are transmitted to ASC-ECU (terminal No.1) via the fusible link No.26.
  • 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 8.

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)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 5.

Go to Step 3.

STEP 3. Check the fusible link No.27

Q. Is the check result normal?
Go to Step 4.
Replace the fusible link No.27.

STEP 4. 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 5. 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)Voltage between the terminal No.1 and the body earth
OK: Approximately battery voltage

Q. Is the check result normal?

Go to Step 17.

Go to Step 6.

STEP 6. Check the fusible link No.26

Q. Is the check result normal?
Go to Step 7.
Replace the fusible link No.26.

STEP 7. 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 8. Check the fuse No.12 and fusible link No.33

Q. Is the check result normal?
Go to Step 9.
Replace the abnormal fuse or fusible link.

STEP 9. Connector check: C-309 ETACS-ECU connector

Q. Is the check result normal?
Go to Step 10.
Repair the defective connector.

STEP 10. Voltage measurement at the C-309 ETACS-ECU connector
(1)Disconnect the ETACS-ECU connector, and then measure the voltage at the harness connector side.
(2)Voltage between the terminal No.1 and the body earth
OK: Approximately battery voltage

Q. Is the check result normal?
Go to Step 11.
Repair the wiring harness between the fusible link No.33 and the C-309 ETACS-ECU connector terminal No.1.

STEP 11. Connector check: C-317 ETACS-ECU connector

Q. Is the check result normal?
Go to Step 12.
Repair the defective connector.

STEP 12. Voltage measurement at the C-317 ETACS-ECU connector
(1)Disconnect the ETACS-ECU connector, and then measure the voltage at the ETACS-ECU side.
(2)Turn the ignition switch to the ON position.
(3)Voltage between the terminal No.6 and the body earth
OK: Approximately battery voltage

Q. Is the check result normal?
Go to Step 14.
Go to Step 13.

STEP 13. Connector check: C-210 ignition switch connector

Q. Is the check result normal?
Go to Step 18.
Repair the wiring harness between the C-210 ignition switch connector terminal No.2 and the C-317 ETACS-ECU connector terminal No.6.

STEP 14. Voltage measurement at the C-317 ETACS-ECU connector
(1)Disconnect the A-04 ABS-ECU connector, and then measure the voltage at the ETACS-ECU connector to the backprobing.
(2)Turn the ignition switch to the ON position.
(3)Voltage between the terminal No.5 and the body earth
OK: Approximately battery voltage

Q. Is the check result normal?
Go to Step 15.
Replace ETACS-ECU (Refer to GROUP 54A - ETACS-ECU ).

STEP 15. Connector check: A-03 ASC-ECU connector, C-37 intermediate connector and C-317 ETACS-ECU connector

Q. Is the check result normal?
Go to Step 16.
Repair the defective connector.

STEP 16. Wiring harness check between the A-03 ASC-ECU connector terminal No.4 and C-317 ETACS-ECU connector terminal No.5

  • Check for open or short circuit.

Q. Is the check result normal?
Go to Step 17.
Repair the wiring harness.

STEP 17. Resistance measurement at 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 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 earth, and between terminal No.47 and body earth.
OK: Continuity exists (2 Ω or less)

Q. Is the check result normal?

Go to Step 18.

Repair the wiring harness.

STEP 18. Battery check
Refer to GROUP 54A - Battery Test .

Q. Is the battery in good condition?
Go to Step 19.
Charge or replace the battery.

STEP 19. Charging system check
Refer to GROUP 16 - Charging System (2000), (2200), (2400) or (3000).

Q. Is the charging system in good condition?
Go to Step 20.
Repair or replace the charging system component(s).

STEP 20. 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 the ASC-ECU (Refer to ).