Inspection Procedure 8: ABS-ECU power supply circuit system























OPERATION



  • The ABS-ECU power supply signal energized by the ignition switch (IG1) is transmitted to ABS-ECU (terminal No. 7) via the multi-purpose fuse No.12.
  • The ABS-ECU power supply and the valve power supply are transmitted to ABS-ECU (terminal No. 26) via the fusible link No. 27.
  • When malfunction occurs in ABS-ECU power supply, the communication with scan tool becomes unavailable.

PROBABLE CAUSES



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

DIAGNOSIS PROCEDURE


STEP 1. Voltage measurement at the A-02 ABS-ECU connector



(1)Disconnect the ABS-ECU connector, connect special tool ABS check harness (MB991974) to the harness-side connector, and then measure the resistance at the special tool connector side.
note Do not connect the special tool ABS check harness (MB991974) to ABS-ECU.
(2)Turn the ignition switch to the ON position.
(3)Measure the voltage between terminal No. 7 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-02 ABS-ECU connector


(1)Disconnect the ABS-ECU connector, connect special tool ABS check harness (MB991974) to the harness-side connector, and then measure the resistance at the special tool connector side.
note Do not connect the special tool ABS check harness (MB991974) to ABS-ECU.
(2)Turn the ignition switch to the ON position.
(3)Measure the voltage between the terminal No. 26 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-02 ABS-ECU connector


Q. Is the check result normal?

Repair the wiring harness between the fusible link No. 27 and the A-02 ABS-ECU connector terminal No. 26.
Repair the defective connector.

STEP 4. Voltage measurement at the A-02 ABS-ECU connector



(1)Disconnect the ABS-ECU connector, connect special tool ABS check harness (MB991974) to the harness-side connector, and then measure the resistance at the special tool connector side.
note Do not connect the special tool ABS check harness (MB991974) to ABS-ECU.
(2)Turn the ignition switch to the ON position.
(3)Voltage between the terminal No. 13 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-02 ABS-ECU connector


Q. Is the check result normal?

Repair the wiring harness between the fusible link No. 26 and the A-02 ABS-ECU connector terminal No. 13.
Repair the defective connector.

STEP 6. Connector check: A-02 ABS-ECU connector, C-37 intermediate connector, C-317 ETACS-ECU connector, C-210 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-02 ABS-ECU connector terminal No. 7 and the C-210 ignition switch connector.
Repair the defective connector.

STEP 7. Wiring harness check between the A-02 ABS-ECU connector terminal No. 1/14 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 scan tool 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 ABS-ECU.