Inspection Procedure 8

Inspection Procedure 8: ABS-ECU power supply circuit system

SYSTEM OPERATION

- ABS-ECU contains the power supply circuit (terminal No. 26) for the solenoid valve. The solenoid valve is energized by the valve relay, which is incorporated in ABS-ECU.

- ABS-ECU contains the power supply circuit (terminal No.13) for the pump motor. The pump motor is energized by the motor relay, which is incorporated in ABS-ECU.

- ABS-ECU contains the power supply circuit (terminal No.7) for ABS-ECU. When the ignition switch (IG1) is turned ON, the voltage is applied to the relay incorporated in ETACS-ECU to turn ON the relay, and the power is supplied from fusible link No.34 through multi-purpose fuse No.12.

- When malfunction occurs in ABS-ECU power supply, the communication with scan tool becomes unavailable.

PROBABLE CAUSES

- Damaged wiring harness and connectors

- Malfunction of fuse and fusible link

- Improper tightening of battery terminal

- Improper tightening of ground bolt

- Battery failure

- Charging system failed

- Malfunction of ABS-ECU

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

- MB991974: ABS check harness

STEP 1. Battery check

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

Generator Output Line Voltage Drop Test.

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-03 ABS-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-03 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)Disconnect the fusible link No.27.
(3)Measure the resistance between the terminal No.26 and the body ground.
OK: No continuity

Q. Is the check result normal?

YES Replace the fusible link No.27. Then go to Step 27.

NO The short circuit may be present in the power supply circuit. Repair the wiring harness between the A-03 ABS-ECU connector terminal No.26 and the fusible link No.27, and then replace the fusible link No.27. Then go to Step 27.

STEP 6. Check the fusible link No.26.

Q. Is the check result normal?

YES Go to Step 8.
NO Go to Step 7.
STEP 7. Resistance measurement at A-03 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)Measure the resistance between the terminal No.13 and the body ground.
OK: No continuity

Q. Is the check result normal?

YES Replace the fusible link No.26. Then go to Step 27.

NO The short circuit may be present in the power supply circuit. Repair the wiring harness between the A-03 ABS-ECU connector terminal No.13 and the fusible link No.26, and then replace the fusible link No.26. Then go to Step 27.

STEP 8. 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 11.
NO Go to Step 9.
STEP 9. Connector check: C-128 intermediate connector, C-317 ETACS-ECU connector

Q. Is the check result normal?

YES Go to Step 10.
NO Repair the defective connector.
STEP 10. Resistance measurement at A-03 ABS-ECU connector

(1)Disconnect the C-317 ETACS-ECU connector.

(2)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.

(3)Measure the resistance between the terminal No.7 and the body ground.
OK: No continuity

Q. Is the check result normal?

YES Replace the fuse No.12. Then go to Step 27.

NO The short circuit may be present in the power supply circuit. Repair the wiring harness between the A-03 ABS-ECU connector terminal No.7 and the C-317 ETACS-ECU connector terminal No.5, and then replace the fuse No.12. Then go to Step 27.

STEP 11. Fusible link check: Check the fusible link No.34.

Q. Is the check result normal?

YES Go to Step 14.
NO Go to Step 12.
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. 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)Measure the 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. Then go to Step 27.
NO The short circuit may be present in the power supply circuit. Repair the wiring harness between the C-309 ETACS-ECU connector terminal No.1 and the fusible link No.34, and then replace the fusible link No.34. Then go to Step 27.
STEP 14. Voltage measurement at the A-03 ABS-ECU connector

(1)Disconnect the ASC-ECU connector, connect special tool ABS check harness (MB991974) to the harness-side connector, and then measure the voltage at the special tool connector side.
NOTE:
Do not connect the special tool ABS check harness (MB991974) to ASC-ECU.

(2)Measure the voltage between terminal No.26 and body ground.
OK: Approximately system voltage

Q. Is the check result normal?

YES Go to Step 15.

NO The open circuit may be present in the power supply circuit. Repair the wiring harness between the A-03 ABS-ECU connector terminal No.26 and the fusible link No.27. Then go to Step 27.

STEP 15. Voltage measurement at the A-03 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 voltage at the special tool connector side.
NOTE:
Do not connect the special tool ABS check harness (MB991974) to ABS-ECU.

(2)Measure the voltage between terminal No.13 and body ground.
OK: Approximately system voltage

Q. Is the check result normal?

YES Go to Step 16.

NO The open circuit may be present in the power supply circuit. Repair the wiring harness between the A-03 ABS-ECU connector terminal No.13 and the fusible link No.26. Then go to Step 27.

STEP 16. Measure the voltage at the C-309 ETACS-ECU connector.

(1)Disconnect the connector, and measure at the wiring harness-side connector.

(2)Measure the voltage between the terminal No.1 and the body ground.
OK: Approximately system voltage

Q. Is the check result normal?

YES Go to Step 17.
NO The open circuit may be present in the power supply circuit. Repair the wiring harness between the C-309 ETACS-ECU connector terminal No.1 and fusible link No.34. Then go to Step 27.
STEP 17. Connector check: C-317 ETACS-ECU connector

Q. Is the check result normal?

YES Go to Step 18.
NO : Repair the damaged connector.
STEP 18. Measure the voltage 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)Measure the voltage between the terminal No.6 and the body ground.
OK: Approximately system voltage

Q. Is the check result normal?

YES Go to Step 21.
NO Go to Step 19.
STEP 19. Connector check: C-212 ignition switch connector

Q. Is the check result normal?

YES Go to Step 20.
NO : Repair the damaged connector.
STEP 20. Check the harness wire between C-212 ignition switch connector terminal No.2 and C-317 ETACS-ECU connector terminal No.6.

- Check the communication lines for open circuit and short circuit.

Q. Is the check result normal?

YES Diagnosis the ignition switch Symptom Chart).
NO Repair the wiring harness, and then go to Step 27.
STEP 21. Measure the voltage at the 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 system voltage

Q. Is the check result normal?

YES Go to Step 23.
NO Go to Step 22.
STEP 22. Check the harness wire between A-03 ABS-ECU connector terminal No.7 and C-317 ETACS-ECU connector terminal No.5.

- Check the harness wire for short circuit.

NOTE:
Prior to the wiring harness inspection, check intermediate connector C-128, and repair if necessary.

Q. Is the check result normal?

YES Replace the ETACS-ECU Electronic Time and Alarm Control System (ETACS)-ECU Removal and Installation), and then go to Step 27.
NO Repair the wiring harness, and then go to Step 27.
STEP 23. Connector check: C-128 intermediate connector

Q. Is the check result normal?

YES Go to Step 24.
NO : Repair the damaged connector.
STEP 24. Voltage measurement at A-03 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)Measure the resistance between the terminal No.1 and the body ground, and between the terminal No.14 and the body ground
OK: Continuity exists (2 ohms or less)

Q. Is the check result normal?

YES Go to Step 26.

NO An open circuit may be present in the ground circuit. Repair the wiring harness between the A-03 ASC-ECU connector terminal No.1 and the body ground, and between the A-03 ASC-ECU connector terminal No.14 and the body ground. Then go to Step 27.

STEP 26. Retest the system.

Make sure that the M.U.T.-III cable is properly connected and the V.C.I. switch is ON,

Q. Is the communication with scan tool possible?

YES Intermittent malfunction How to Cope With Intermittent Malfunctions).
NO Replace the hydraulic unit (integrated with ABS-ECU) (Refer to Anti-Lock Braking System (ABS)). Then go to Step 27.
STEP 27. Retest the system.

Q. Is the communication with scan tool possible?

YES Return to Step 1.
NO The procedure is complete.