Inspection Procedure
7: ABS-ECU power supply circuit system
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 ABS-ECU
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Refer to GROUP 54A - Battery Test .
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Q.
Is the battery in good condition?
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Go to Step 3.
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Charge or replace the battery. Then go to Step 2.
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STEP 2. Charging system check
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Refer to GROUP 16 - On-vehicle Service, Alternator Output Line Voltage
Drop Test .
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Q.
Is the charging system in good condition?
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Go to Step 3.
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Repair or replace the charging system component(s).
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STEP 3. Connector check: ABS-ECU connector
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Q.
Is the check result normal?
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Go to Step 4.
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NO : Repair the damaged connector.
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STEP 4. Check the fuse (relay box).
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Q.
Is the check result normal?
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Go to Step 6.
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Go to Step 5.
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STEP 5. Resistance measurement at ABS-ECU connector
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(1)Disconnect the ABS-ECU connector.
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(2)Removal the fuse (relay box).
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(3)Measure the resistance between the +BV terminal and the body earth. OK: No continuity
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Q.
Is the check result normal?
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Replace the fuse (relay box). Then go to Step 17.
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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.
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STEP 6. Check the fusible link.
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Q.
Is the check result normal?
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Go to Step 8.
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Go to Step 7.
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STEP 7. Resistance measurement at ABS-ECU connector
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(1)Disconnect the ABS-ECU connector.
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(2)Measure the resistance between the +BM terminal and the body earth. OK: No continuity
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Q.
Is the check result normal?
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Replace the fusible link. Then go to Step 17.
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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.
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STEP 8. Check the fuse (junction block).
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Visually check for open circuit in fuse.
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Q.
Is the check result normal?
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Go to Step 10.
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Go to Step 9.
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STEP 9. Resistance measurement at ABS-ECU connector
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(1)Disconnect the junction block connector.
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(2)Disconnect the ABS-ECU connector.
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(3)Measure the resistance between the IG1 terminal and the body earth. OK: No continuity
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Q.
Is the check result normal?
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Replace the fuse. Then go to Step 17.
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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.
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STEP 10. Voltage measurement at the ABS-ECU connector
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(1)Disconnect the ABS-ECU connector.
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(2)Measure the voltage between +BV terminal and body earth. OK: Approximately system voltage
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Q.
Is the check result normal?
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Go to Step 11.
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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.
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STEP 11. Voltage measurement at the ABS-ECU connector
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(1)Disconnect the ABS-ECU connector.
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(2)Measure the voltage between +BM terminal and body earth. OK: Approximately system voltage
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Q.
Is the check result normal?
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Go to Step 12.
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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.
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STEP 12. Measure the voltage at the junction block connector.
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(1)Measure by backprobing without disconnecting the junction block connector.
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(2)Disconnect the ABS-ECU connector.
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(3)Turn the ignition switch to the "ON" position.
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(4)Measure the voltage between terminal ABS-ECU IG1 line and the body earth. OK: Approximately system voltage
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Q.
Is the check result normal?
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Go to Step 14.
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Go to Step 13.
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STEP 13. Check the harness wire between ABS-ECU connector IG1 terminal
and junction block connector terminal.
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- Check the harness wire for short circuit.
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Q.
Is the check result normal?
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Replace the junction block, and then go to Step 17.
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Repair the damaged connector, or repair the wiring harness, and then go to Step
17.
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STEP 14. Voltage measurement at ABS-ECU connector
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(1)Disconnect the ABS-ECU connector.
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(2)Turn the ignition switch to the "ON" position.
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(3)Measure the voltage between IG1 terminal and body earth. OK: Approximately system voltage
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Q.
Is the check result normal?
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Go to Step 15.
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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.
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STEP 15. Resistance measurement at ABS-ECU connector
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(1)Disconnect the ABS-ECU connector.
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(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)
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Q.
Is the check result normal?
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Go to Step 16.
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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.
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STEP 16. Retest the system.
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Make sure that the M.U.T.-III cable is properly connected and the V.C.I. switch is "ON".
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Q.
Is the communication with M.U.T.-III possible?
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Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting,
How to Cope with Intermittent Malfunction .)
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Replace the hydraulic unit [(integrated with ABS-ECU) Refer to ].
Then go to Step 17.
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STEP 17. Retest the system.
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Q.
Is the communication with M.U.T.-III possible?
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Return to Step 1.
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This diagnosis is complete.
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