Inspection Procedure 5: ABS-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 - CAN Bus Diagnostics Table ).
Whenever ECU is replaced, ensure that the CAN bus lines are normal.

OPERATION

ABS-ECU contains the power supply circuit (+BV terminal) 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 (+BM terminal) 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 (IG1 terminal) for ABS-ECU. When the ignition switch (IG1) is turned "ON", the power is supplied from fusible link through multi-purpose fuse.
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 the hydraulic unit assembly (integrated with 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 - On-vehicle Service, Alternator Output Line Voltage Drop Test

Q. Is the charging system in good condition?

	Go to Step 3.

	Repair or replace the charging system component(s).

STEP 3. Connector check: ABS-ECU connector

Q. Is the check result normal?

	Go to Step 4.

	NO : Repair the damaged connector.

STEP 4. Check the fuse (relay box).

Q. Is the check result normal?

	Go to Step 6.

	Go to Step 5.

STEP 5. Resistance measurement at ABS-ECU connector

(1)Disconnect the ABS-ECU connector.

(2)Removal the fuse (relay box).

(3)Measure the resistance between the +BV terminal and the body earth.
OK: No continuity

Q. Is the check result normal?

	Replace the fuse (relay box). Then go to Step 17.

	The short circuit may be present in the power supply circuit. Repair the wiring harness between the ABS-ECU connector +BV terminal and the fuse (relay box), and then replace the fuse (relay box). Then go to Step 17.

STEP 6. Check the fusible link.

Q. Is the check result normal?

	Go to Step 8.

	Go to Step 7.

STEP 7. Resistance measurement at ABS-ECU connector

(1)Disconnect the ABS-ECU connector.

(2)Measure the resistance between the +BM terminal and the body earth.
OK: No continuity

Q. Is the check result normal?

	Replace the fusible link. Then go to Step 17.

	The short circuit may be present in the power supply circuit. Repair the wiring harness between the ABS-ECU connector +BM terminal and the fusible link, and then replace the fusible link. Then go to Step 17.

STEP 8. Check the fuse (junction block).

Visually check for open circuit in fuse.

Q. Is the check result normal?

	Go to Step 10.

	Go to Step 9.

STEP 9. Resistance measurement at ABS-ECU connector

(1)Disconnect the junction block connector.

(2)Disconnect the ABS-ECU connector.

(3)Measure the resistance between the IG1 terminal and the body earth.
OK: No continuity

Q. Is the check result normal?

	Replace the fuse. Then go to Step 17.

	Repair the damaged connector. The short circuit may be present in the power supply circuit. Repair the wiring harness between the ABS-ECU connector IG1 terminal and the junction block connector, and then replace the fuse. Then go to Step 17.

STEP 10. Voltage measurement at the ABS-ECU connector

(1)Disconnect the ABS-ECU connector.

(2)Measure the voltage between +BV terminal and body earth.
OK: Approximately system voltage

Q. Is the check result normal?

	Go to Step 11.

	The open circuit may be present in the power supply circuit. Repair the wiring harness between the ABS-ECU connector +BV terminal and the fuse (relay box). Then go to Step 17.

STEP 11. Voltage measurement at the ABS-ECU connector

(1)Disconnect the ABS-ECU connector.

(2)Measure the voltage between +BM terminal and body earth.
OK: Approximately system voltage

Q. Is the check result normal?

	Go to Step 12.

	The open circuit may be present in the power supply circuit. Repair the wiring harness between the ABS-ECU connector +BM terminal and the fusible link. Then go to Step 17.

STEP 12. Measure the voltage at the junction block connector.

(1)Measure by backprobing without disconnecting the junction block connector.

(2)Disconnect the ABS-ECU connector.

(3)Turn the ignition switch to the "ON" position.

(4)Measure the voltage between terminal ABS-ECU IG1 line and the body earth.
OK: Approximately system voltage

Q. Is the check result normal?

	Go to Step 14.

	Go to Step 13.

STEP 13. Check the harness wire between ABS-ECU connector IG1 terminal and junction block connector terminal.

Check the harness wire for short circuit.

Q. Is the check result normal?

	Replace the junction block, and then go to Step 17.

	Repair the damaged connector, or repair the wiring harness, and then go to Step 17.

STEP 14. Voltage measurement at ABS-ECU connector

(1)Disconnect the ABS-ECU connector.

(2)Turn the ignition switch to the "ON" position.

(3)Measure the voltage between IG1 terminal and body earth.
OK: Approximately system voltage

Q. Is the check result normal?

	Go to Step 15.

	Repair the damaged connector. The open circuit may be present in the power supply circuit. Repair the wiring harness between the ABS-ECU connector IG1 terminal and the junction block connector terminal. Then go to Step 17.

STEP 15. Resistance measurement at ABS-ECU connector

(1)Disconnect the ABS-ECU connector.

(2)Measure the resistance between the GND1 terminal and the body earth, and between the GND2 terminal and the body earth
OK: Continuity exists (2 Ω or less)

Q. Is the check result normal?

	Go to Step 16.

	An open circuit may be present in the earth circuit. Repair the wiring harness between the ABS-ECU connector GND1 terminal and the body earth, and between the ABS-ECU connector GND2 terminal and the body earth. Then go to Step 17.

STEP 16. 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 M.U.T.-III possible?

	Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting, How to Cope with Intermittent Malfunction ).

	Replace the hydraulic unit assembly (integrated with ABS-ECU) (Refer to ). Then go to Step 17.

STEP 17. Retest the system.

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

	Return to Step 1.

	This diagnosis is complete.