DTC P0638: Throttle Valve Control Servo Circuit Range/Performance Problem

OPERATION

• Controls the current that is applied from the engine-ECU (terminal No. 7 and No. 22) to the electronic-controlled throttle valve (terminals No. 1 and No. 2).
  
• The engine-ECU (terminal No. 93 and No. 108 is earthed to the vehicle body)
  

FUNCTION

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

TROUBLE JUDGMENT

• Battery positive voltage is 8.3 V or higher.
  
• Throttle position sensor (main) output voltage is 0.35 - 4.8 V.
  
• Drop of throttle position sensor (main) output voltage per 100 milliseconds is 0.04 V or more.
  

• Throttle position sensor (main) output voltage has continued to be above 0.5 V higher than the target throttle position sensor (main) voltage for 0.5 second.
  

• Battery positive voltage is 8.3 V or higher.
  
• Throttle position sensor (main) output voltage is 0.35 - 4.8 V.
  

• Difference between throttle position sensor (main) output voltage and target throttle position sensor (main) voltage is 1 V or higher for 4 seconds.
  

PROBALE CAUSES

• Failed throttle valve operation.
  
• Failed throttle valve control servo.
  
• Open or shorted throttle valve control servo circuit, harness damage, or connector damage
  
• Failed engine-ECU
  

	Go to Step 2 .

	Replace electronically controlled throttle valve.

Q. Is the check result normal? Go to Step 3 . Repair or replace the connector.

Disconnect connector, and measure at harness side. Resistance between terminal No. 93 and earth, also between or terminal No. 108 and earth. OK: Continuity (2 Ω or less) Q. Is the check result normal? Go to Step 4 . Check intermediate connector A-14 and repair if necessary. If intermediate connector is normal, check and repair harness between engine-ECU or connector and body earth Check and repair harness between A-08 (terminal No. 93) engine-ECU connector and body earth. Check and repair harness between A-08 (terminal No. 108) engine-ECU connector and body earth.

Check output line for short circuit and damage. Q. Is the check result normal? Go to Step 5 . Repair the damaged harness wire.

Check output line for short circuit and damage. Q. Is the check result normal? Go to Step 6 . Repair the damaged harness wire.

	Replace the engine-ECU then perform the variant coding (Refer to GROUP 00 - Precautions Before Service - How to Perform Variant Coding ).

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