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










OPERATION



  • The electric current from the engine-ECU (terminal No. 15 and No. 16) to the throttle valve control servo (terminal No. 1 and No. 2) is controlled.

FUNCTION



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

TROUBLE JUDGMENT


Check Conditions
  • Battery positive voltage is higher than 8.3 V.
  • Throttle position sensor (main) output voltage is 0.2 - 4.8 V.
  • Drop of throttle position sensor (main) output voltage per 100 milliseconds is more than 0.04 V.
Judgment Criterion
  • Throttle position sensor (main) output voltage has continued to be higher than the target throttle position sensor (main) voltage by 0.5 V or more.
Check Conditions
  • Battery positive voltage is higher than 8.3 V.
  • Throttle position sensor (main) output voltage is 0.2 - 4.8 V.
  • Drop of throttle position sensor (main) output voltage per 100 milliseconds is more than 0.04 V.
  • Target throttle position sensor (main) output voltage is 1.5 V or lower.
Judgment Criteria
  • Difference between throttle position sensor (main) output voltage and target throttle position sensor (main) voltage is 0.6 V or higher.
  • Throttle position sensor (main) output voltage has continued to be higher than the target throttle position sensor (main) voltage by 0.5 V or more for 0.5 second.
Check Conditions
  • Battery positive voltage is higher than 8.3 V.
  • Throttle position sensor (main) output voltage is 0.2 - 4.8 V.
Judgment Criterion
  • Difference between throttle position sensor (main) output voltage and target throttle position sensor (main) voltage is 1 V or higher.
Check Condition
  • Battery positive voltage is higher than 8.3 V.
Judgment Criterion
  • Throttle position sensor (main) default opening learnt value is higher than 4 V or higher for 1 second.

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.



  • Check throttle valve control servo (Refer to ).

Q. Is the check result normal?

Go to Step 3 .
Replace the throttle body assembly.

STEP 3. Connector check: B-20 electronic controlled throttle valve connector


Q. Is the check result normal?

Go to Step 4 .
Repair or replace the connector.

STEP 4. Connector check: B-29 engine-ECU connector


Q. Is the check result normal?

Go to Step 5 .
Repair or replace the connector.

STEP 5. Check harness between B-20 (terminal No. 1) electronic controlled throttle valve connector and B-29 (terminal No. 15) engine-ECU connector.



  • Check signal line for damage.

Q. Is the check result normal?

Go to Step 6 .
Repair the damaged harness wire.

STEP 6. Check harness between B-20 (terminal No. 2) electronic controlled throttle valve connector and B-29 (terminal No. 16) engine-ECU connector.



  • Check signal line for damage.

Q. Is the check result normal?

Go to Step 7 .
Repair the damaged harness wire.

STEP 7. M.U.T.-III diagnosis code



  • Reconfirmation of diagnosis code.

Q. Is diagnosis code set?

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