Inspection Procedure
12: ASTC-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.
- When the hydraulic unit (integrated with ASTC-ECU) is replaced, always carry out
the calibration of the master cylinder pressure sensor, steering wheel sensor and the G and yaw
rate sensor (Refer to
).
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OPERATION
- The ASTC-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 the ASTC-ECU.
- The ASTC-ECU contains the power supply circuit (+BM terminal) for the pump
motor. The pump motor is energized by the motor relay, which is incorporated in the ASTC-ECU.
- The ASTC-ECU contains the power supply circuit (IG1 terminal) for itself. When the
ignition switch (IG1) is turned ON, the voltage is applied to the relay incorporated in the
ETACS-ECU to turn ON the relay, and the power is supplied from the fusible link through the
multi-purpose fuse.
- When malfunction occurs in ASTC-ECU power supply, the communication with M.U.T.-III becomes
unavailable.
PROBABLE CAUSES
- Battery failure
- Improper tightening of battery terminal
- Charging system failed
- Damaged harness wires and connectors
- Fuse and fusible link malfunction
- Improper tightening of earth bolt
- Malfunction of the hydraulic unit assembly (integrated with ASTC-ECU)
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STEP 1. Check the battery.
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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. Check the charging system.
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Refer to GROUP 16 - Charging System .
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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. Measure the resistance at the ASTC-ECU connector.
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(1)Connector check: the ASTC-ECU connector, the fuses (relay box) and the fusible
links
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(2)Disconnect the ASTC-ECU connector.
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(3)Measure the resistance between +BV terminal and body earth. OK: No continuity
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Q.
Is the check result normal?
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Go to Step 4.
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The power supply circuit may be short. Repair the wiring harness wires or connectors
between the ASTC-ECU connector +BV terminal and the fuse (relay box), the fuses (relay
box) or the fusible links. Then go to Step 11.
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STEP 4. Measure the resistance at the ASTC-ECU connector.
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(1)Connector check: the ASTC-ECU connector and the fusible links
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(2)Disconnect the ASTC-ECU connector and remove the fusible links.
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(3)Measure the resistance between +BM terminal and body earth. OK: No continuity
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Q.
Is the check result normal?
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Go to Step 5.
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The power supply circuit may be short. Repair the wiring harness wires or connectors
between the ASTC-ECU connector +BM terminal and the fusible links, or the fusible links.
Then go to Step 11.
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STEP 5. Measure the resistance at the ASTC-ECU connector.
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(1)Connector check: the ASTC-ECU connector and the junction block
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(2)Disconnect the ASTC-ECU connector.
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(3)Measure the resistance between the IG1 terminal and body earth. OK: No continuity
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Q.
Is the check result normal?
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Go to Step 6.
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The power supply circuit may be short. Repair the wiring harness wires or connectors
between the ASTC-ECU connector IG1 terminal and the junction block. Then go to Step 11.
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STEP 6. Measure the voltage at the ASTC-ECU connector.
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(1)Disconnect the ASTC-ECU connector.
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(2)Measure the voltage between +BV terminal and body earth. OK: Battery voltage
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Q.
Is the check result normal?
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Go to Step 7.
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The power supply circuit may be open. Repair the wiring harness wires or connectors
between the ASTC-ECU connector +BV terminal and the fuse (relay box) or the fuses (relay
box). Then go to Step 11.
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STEP 7. Measure the voltage at the ASTC-ECU connector.
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(1)Disconnect the ASTC-ECU connector.
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(2)Measure the voltage between +BM terminal and body earth. OK: Battery voltage
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Q.
Is the check result normal?
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Go to Step 8.
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The power supply circuit may be open. Repair the wiring harness wires or connectors
between the ASTC-ECU connector +BM terminal and the fusible links, or the fusible links.
Then go to Step 11.
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STEP 8. Measure the voltage at the ASTC-ECU connector.
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(1)Disconnect the ASTC-ECU connector.
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(3) Measure the voltage between the IG1 terminal and body earth. OK: Battery voltage
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Q.
Is the check result normal?
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Go to Step 9.
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The power supply circuit may be open. Repair the wiring harness wires or connectors
between the ASTC-ECU connector IG1 terminal and the junction block. Then go to Step 11.
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STEP 9. Measure the resistance at the ASTC-ECU connector.
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(1)Disconnect the ASTC-ECU connector.
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(2) Measure the resistance between the GND1 terminal and body earth as well as between
the GND2 terminal and 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 10.
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The earth circuit may be open. Repair the wiring harness wires or connectors between
the ASTC-ECU connector GND1 terminal and the fusible links as well as between the GND2 terminal
and the fusible links. Then go to Step 11.
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STEP 10. 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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The trouble can be an intermittent malfunction (Refer to GROUP 00 - How
to Cope with Intermittent Malfunction ).
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Replace the hydraulic unit assembly (integrated with ASTC-ECU) (Refer to ).
Then go to Step 11.
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STEP 11. 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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