Inspection Procedure 8: ABS-ECU power supply circuit system

OPERATION

ABS-ECU contains the power supply circuit (terminal No. 26) for the solenoid valve. The solenoid valve is energised 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 energised 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 <4A9, 4B1> or No.44 <BWC> through multi-purpose fuse No.12.
When malfunction occurs in ABS-ECU power supply, the communication with M.U.T.-III becomes unavailable.

PROBABLE CAUSES

Damaged wiring harness and connectors
Malfunction of fuse and fusible link
Improper tightening of battery terminal
Improper tightening of earth bolt
Battery failure
Charging system failed
Malfunction of ABS-ECU

DIAGNOSIS PROCEDURE

STEP 1. Battery check

Refer to GROUP 54A - Battery Test

Q. Is the battery in good condition?

	Go to Step 3.

	Charge or replace the battery. Then go to Step 2.

STEP 2. Charging system check

Refer to GROUP 16 - Charging System

<4A9, 4B1>

<BWC>.

Q. Is the charging system in good condition?

	Go to Step 3.

	Repair or replace the charging system component(s).

STEP 3. Connector check: A-04 ABS-ECU connector

Q. Is the check result normal?

	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?

	Go to Step 6.

	Go to Step 5.

STEP 5. Resistance measurement at A-04 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)Removal the fusible link No.27.
(3)Resistance between the terminal No.26 and the body earth.
OK: No continuity

Q. Is the check result normal?

Replace the fusible link No.27. Then go to Step 24.

The short circuit may be present in the power supply circuit. Repair the wiring harness between the A-04 ABS-ECU connector terminal No.26 and the fusible link No.27, and then replace the fusible link No.27. Then go to Step 24.

STEP 6. Fusible link check: Check the fusible link No.26.

Visually check for open circuit in the fusible link No.26.

Q. Is the check result normal?

	Go to Step 8.

	Go to Step 7.

STEP 7. Resistance measurement at A-04 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)Resistance between the terminal No.13 and the body earth.
OK: No continuity

Q. Is the check result normal?

Replace the fusible link No.26. Then go to Step 24.

The short circuit may be present in the power supply circuit. Repair the wiring harness between the A-04 ABS-ECU connector terminal No.13 and the fusible link No.26, and then replace the fusible link No.26. Then go to Step 24.

STEP 8. Check the fuse No.12.

Visually check for open circuit in fuse No.12.

Q. Is the check result normal?

	Go to Step 11.

	Go to Step 9.

STEP 9. Connector check: C-128 intermediate connector, C-317 ETACS-ECU connector

Q. Is the check result normal?

	Go to Step 10.

	NO : Repair the damaged connector.

STEP 10. Resistance measurement at A-04 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)Resistance between the terminal No.7 and the body earth.
OK: No continuity

Q. Is the check result normal?

Replace the fuse No.12. Then go to Step 24.

The short circuit may be present in the power supply circuit. Repair the wiring harness between the A-04 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 24.

STEP 11. Fusible link check: Check the fusible link No.34 <4A9, 4B1> or No.44 <BWC>.

Q. Is the check result normal?

	Go to Step 14.

	Go to Step 12.

STEP 12. Connector check: C-309 ETACS-ECU connector

Q. Is the check result normal?

	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 <4A9, 4B1> or No.44 <BWC>.

(2)Disconnect the C-309 ETACS-ECU connector, and then measure the resistance at the connector side.

(3)Resistance between the terminal No.1 and the body earth.
OK: No continuity

Q. Is the check result normal?

	Replace the fusible link No.34 <4A9, 4B1> or No.44 <BWC>. Then go to Step 24.

	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 <4A9, 4B1> or No.44 <BWC>, and then replace the fusible link No.34 <4A9, 4B1> or No.44 <BWC>. Then go to Step 24.

STEP 14. Voltage measurement at the A-04 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.26 and body earth.
OK: Approximately battery voltage

Q. Is the check result normal?

Go to Step 15.

The open circuit may be present in the power supply circuit. Repair the wiring harness between the A-04 ABS-ECU connector terminal No.26 and the fusible link No.27. Then go to Step 24.

STEP 15. 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 earth.
OK: Approximately battery voltage

Q. Is the check result normal?

	Go to Step 16.

	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 <4A9, 4B1> or No.44 <BWC>. Then go to Step 24.

STEP 16. Connector check: C-317 ETACS-ECU connector

Q. Is the check result normal?

	Go to Step 17.

	NO : Repair the damaged connector.

STEP 17. 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 earth.
OK: Approximately battery voltage

Q. Is the check result normal?

	Go to Step 19.

	Go to Step 18.

STEP 18. Connector check: C-212 ignition switch connector

Q. Is the check result normal?

	Repair the wiring harness between C-212 ignition switch connector terminal No.2 and C-317 ETACS-ECU connector terminal No.6. Then go to Step 24.

	NO : Repair the damaged connector.

STEP 19. 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 earth by backprobing.
OK: Approximately battery voltage

Q. Is the check result normal?

	Go to Step 20.

	Replace the ETACS-ECU (Refer to GROUP 54A - ETACS-ECU .) Then go to Step 24.

STEP 20. Connector check: C-128 intermediate connector

Q. Is the check result normal?

	Go to Step 21.

	NO : Repair the damaged connector.

STEP 21. Voltage measurement at A-04 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 22.

The open circuit may be present in the power supply circuit. Repair the wiring harness between the A-04 ABS-ECU connector terminal No.7 and the C-317 ETACS-ECU connector terminal No.5. Then go to Step 24.

STEP 22. Resistance measurement at A-04 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)Resistance between the terminal No.1 and the body earth, and between the terminal No.14 and the body earth
OK: Continuity exists (2 Ω or less)

Q. Is the check result normal?

Go to Step 23.

An open circuit may be present in the earth circuit. Repair the wiring harness between the A-04 ABS-ECU connector terminal No.1 and the body earth, and between the A-04 ABS-ECU connector terminal No.14 and the body earth. Then go to Step 24.

STEP 23. 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 ABS-ECU (Refer to ). Then go to Step 24.

STEP 24. Retest the system.

Q. Is the communication with M.U.T.-III possible?

	Return to Step 1.

	This diagnosis is complete.