To judge whether fail-safe control can be performed, check that power supply to the throttle valve control servo circuit can be stopped by turning the throttle valve control servo relay to OFF position momentarily.
TROUBLE JUDGEMENT
Check Condition
Ignition switch is "ON" position.
Judgement Criterion
Power supply to the throttle valve control servo cannot be shut down (though power supply is stopped).
FAIL-SAFE AND BACKUP FUNCTION
Microcomputer is reset.
PROBABLE CAUSES
Failed throttle valve control servo relay circuit
Failed engine-ECU
DIAGNOSIS PROCEDURE
STEP 1. M.U.T.-III diagnosis code
Reconfirmation of diagnosis code.
Q.
Is diagnosis code set?
Go to Step 2.
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).
STEP 2. M.U.T.-III diagnosis code
Q.
Is diagnosis code P0657 set?
Check throttle valve control servo power system. Check code No. P0657: throttle valve control servo relay circuit malfunction (Refer to ).