Inspection Procedure 1: Steering wheel sensor power supply system.
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When the steering wheel sensor is replaced, always carry out calibration to make ASTC-ECU learn the neutral point (Refer to  ).
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OPERATION
- The steering wheel sensor contains the power supply circuit (IG 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 steering wheel sensor 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 column switch assembly (Integrated with steering wheel sensor)
DIAGNOSIS PROCEDURE
STEP 1. Check the battery.
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. Check the charging system.
Refer to GROUP 16 - Charging System .
Q.
Is the charging system in good condition?
Go to Step 3.
Repair or replace the charging system component(s).
STEP 3. Measure the resistance at the column switch connector.
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(1)Connector check: the column switch connector and the junction block
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(2)Disconnect the column switch connector.
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(3)Measure the resistance between the IG terminal and body earth.
OK: No continuity
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Q.
Is the check result normal?
Go to Step 4.
The power supply circuit may be short. Repair the wiring harness wires or connectors between the column switch connector IG terminal and the junction block. Then go to Step 7.
STEP 4. Measure the voltage at the column switch connector.
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(1)Disconnect the column switch connector.
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(3) Measure the voltage between the IG terminal and body earth.
OK: System voltage
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Q.
Is the check result normal?
Go to Step 5.
The power supply circuit may be open. Repair the wiring harness wires or connectors between the column switch connector IG terminal and the junction block. Then go to Step 7.
STEP 5. Measure the resistance at the column switch connector.
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(1)Disconnect the column switch connector.
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(2) Measure the resistance between the GND terminal and body earth.
OK: Continuity exists (2 Ω or less).
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Q.
Is the check result normal?
Go to Step 6.
The earth circuit may be open. Repair the wiring harness wires or connectors between the column switch connector GND terminal and body earth. Then go to Step 7.
STEP 6. 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?
The trouble can be an intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent Malfunction ).
Replace the column switch assembly (Integrated with steering wheel sensor) (Refer to GROUP 54A - Column Switch ).
STEP 7. Retest the system
Q.
Is the communication with M.U.T.-III possible?
This diagnosis is complete.
Replace the column switch assembly (Integrated with steering wheel sensor) (Refer to GROUP 54A - Column Switch ).