Inspection Procedure
8: ABS-ECU power supply circuit system
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- When the ABS-ECU
power supply voltage becomes 9.7 ±
0.3 V or less, the ABS warning lamp illuminate,
and the ABS control is prohibited.
- If the battery terminal is not tightened properly, a dump surge may occur and the
power supply voltage may become abnormally high for a short time.
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- 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 voltage is applied to the relay incorporated in ETACS-ECU to
turn ON the relay, and 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.
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- 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. M.U.T.-III other system diagnosis code
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Check if diagnosis code is set to the ETACS-ECU.
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Q.
Is the diagnosis code set?
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Troubleshoot the ETACS. Refer to GROUP 54A - ETACS .
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Go to Step 4.
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STEP 4. Voltage measurement at the ABS-ECU connector
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(1)Disconnect the connector, and measure at the wiring harness side.
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(2)Measure the voltage between ABS-ECU (+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 6.
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Go to Step 5.
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STEP 5. Check of short to power supply, short to earth, and open circuit
in +BV line between fusible link and ABS-ECU connector
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Q.
Is the check result normal?
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Intermittent malfunction is suspected (Refer to GROUP 00 -
How to Use
Troubleshooting/Inspection Service Points -
How to Cope with Intermittent Malfunction ).
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Repair the fusible link, connector(s) or wiring harness. Then go to Step 13.
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STEP 6. Voltage measurement at the ABS-ECU connector
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(1)Disconnect the connector, and measure at the wiring harness side.
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(2)Measure the voltage between ABS-ECU (+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 8.
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Go to Step 7.
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STEP 7. Check of short to power supply, short to earth, and open circuit
in +BM line between fusible link and ABS-ECU connector
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Q.
Is the check result normal?
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Intermittent malfunction is suspected (Refer to GROUP 00 -
How to Use
Troubleshooting/Inspection Service Points -
How to Cope with Intermittent Malfunction ).
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Repair the fusible link, connector(s) or wiring harness. Then go to Step 13.
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STEP 8. Voltage measurement at the ABS-ECU connector.
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(1)Disconnect the connector, and measure at the wiring harness side.
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(2)Turn the ignition switch to the ON position.
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(3)Measure the voltage between ABS-ECU (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 10.
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Go to Step 9.
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STEP 9. Check of short to power supply, short to earth, and open circuit
in IG1 line between ETACS-ECU and ABS-ECU connector
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Q.
Is the check result normal?
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Intermittent malfunction is suspected (Refer to GROUP 00 -
How to Use
Troubleshooting/Inspection Service Points -
How to Cope with Intermittent Malfunction ).
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Repair the connector(s) or wiring harness. Then go to Step 13.
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STEP 10. Resistance measurement at ABS-ECU connector
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(1)Disconnect the connector, and measure at the wiring harness side.
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(2)Resistance between the ABS-ECU (GND1 terminal) and the body earth, and between
the ABS-ECU (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 12.
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Go to Step 11.
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STEP 11. Check of open circuit in GND1, GND2 line between ABS-ECU
connector and body earth
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Q.
Is the check result normal?
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Intermittent malfunction is suspected (Refer to GROUP 00 -
How to Use
Troubleshooting/Inspection Service Points -
How to Cope with Intermittent Malfunction ).
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Repair the connector(s) or wiring harness. Then go to Step 13.
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STEP 12. Retest the system.
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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 Malfunctions ).
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Replace the hydraulic unit (integrated with ABS-ECU) (Refer to ). Then
go to Step 13.
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STEP 13. 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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