Code No. P0638: Throttle Valve Control Servo Circuit Range/Performance Problem

OPERATION

The electric current from the engine-ECU connector terminals ETV+, ETV- to the throttle valve control servo is controlled.

FUNCTION

Engine-ECU checks the electronic controlled throttle system for abnormal conditions.

TROUBLE JUDGEMENT

Check Conditions

Battery positive voltage is more than 8.3 V.
Throttle position sensor (main) output voltage is more than 0.2 V and is less than 4.8 V.
Drop of throttle position sensor (main) output voltage per 100 milliseconds is more than 0.04 V.

Judgement Criterion

Throttle position sensor (main) output voltage is higher than the target throttle position sensor (main) voltage by more than 0.5 V.

Check Conditions

Battery positive voltage is more than 8.3 V.
Throttle position sensor (main) output voltage is more than 0.2 V and is less than 4.8 V.
Target throttle position sensor (main) output voltage is less than 1.5 V.

Judgement Criteria

Difference between throttle position sensor (main) output voltage and target throttle position sensor (main) voltage is more than 0.6 V.
Throttle position sensor (main) output voltage has continued to be higher than the target throttle position sensor (main) voltage by more than 0.5 V.

Check Conditions

Battery positive voltage is more than 8.3 V.
Throttle position sensor (main) output voltage is more than 0.2 V and is less than 4.8 V.

Judgement Criterion

Difference between throttle position sensor (main) output voltage and target throttle position sensor (main) voltage is more than 1 V.

Check Condition

Battery positive voltage is more than 8.3 V.

Judgement Criterion

Throttle position sensor (main) default opening learnt value is more than 4 V.

FAIL-SAFE AND BACKUP FUNCTION

Throttle opening degree position is in default position.

PROBABLE CAUSES

Failed throttle valve return spring
Failed throttle valve operation
Failed throttle valve control servo
Harness damage in throttle valve control servo circuit or loose connector contact
Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. Check throttle body.

Check whether the throttle valve return spring is normal.

Q. Is the check result normal?

	Go to Step 2.

	Replace the throttle body assembly.

STEP 2. Check throttle valve control servo itself.

Throttle valve control servo check (Refer to ).

Q. Is the check result normal?

	Go to Step 3.

	Replace the throttle body assembly.

STEP 3. Check of harness damage in ETV+ line between electronic controlled throttle valve connector and engine-ECU connector.

Q. Is the check result normal?

	Go to Step 4.

	Repair the connector(s) or wiring harness.

STEP 4. Check of harness damage in ETV- line between electronic controlled throttle valve connector and engine-ECU connector.

Q. Is the check result normal?

	Go to Step 5.

	Repair the connector(s) or wiring harness.

STEP 5. M.U.T.-III diagnosis code

Reconfirmation of diagnosis code.

Q. Is diagnosis code stored?

	Replace the engine-ECU.

	Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).