Inspection Procedure
12: ASC-ECU power supply circuit system.
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caution |
- When the ASC-ECU
power supply voltage becomes 9.7 ± 0.3 V or less, the ABS warning lamp, ASC warning display,
and ASC OFF display illuminate, and the ABS, stability control, and TCL controls are 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.
- 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.
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- ASC-ECU contains the power supply circuit (+BV
terminal) for the solenoid valve. The solenoid valve is energized by the valve relay, which
is incorporated in ASC-ECU.
- ASC-ECU contains the power supply circuit (IG1 terminal) for ASC-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 the fusible link.
- ASC-ECU contains the power supply circuit (+BM terminal) for the pump motor.
The pump motor is energised by the motor switch, which is incorporated in ASC-ECU.
- When malfunction occurs in ASC-ECU power supply, the communication with M.U.T.-III
becomes unavailable.
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- Damaged wiring harness and connectors
- Fusible link malfunction
- Improper tightening of battery terminal
- Improper tightening of earth bolt
- Battery failure
- Charging system failed
- ASC-ECU malfunction
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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 ASC-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 ASC-ECU connector (+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 ASC-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 ASC-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 ASC-ECU connector (+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 ASC-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 ASC-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 ASC-ECU connector (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 ASC-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 ASC-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 ASC-ECU connector (GND1 terminal) and the body earth, and
between the ASC-ECU connector (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 ASC-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 ASC-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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