P0638Generic code

P0638 Code: Throttle Actuator Control Range/Performance (Bank 1)

The P0638 code means the electronic throttle is not following the position the computer is asking for. The most common cause is carbon buildup or a worn throttle body motor. It usually puts the vehicle into limp mode.

Severity
High
Can I keep driving?
Yes, but with caution
Estimated cost
$0 to $600
Difficulty
Medium
System
Air and Fuel
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P0638 code means

On electronic throttles, a small motor opens and closes the throttle plate, and two sensors report its position. The computer compares the position it asked for with the real one. If the difference stays, it stores the P0638 code and limits engine power for safety.

Carbon that builds up around the throttle plate makes it stick, especially when closing. Over time the gears and the internal motor also wear out.

After you clean or replace the throttle body, you have to run the throttle position relearn.

P0638 code symptoms

  • Limp mode: the vehicle does not accelerate.
  • Unstable or high idle.
  • Check engine light or the power control warning light on.

Likely causes of the P0638 code

  1. Carbon on the throttle plate. The most frequent cause.
  2. Worn motor or gears in the throttle body. They cannot reach the position that is requested.
  3. Corroded connector. It raises the resistance of the signals.
  4. Position sensor built into the throttle body.

How to diagnose the P0638 code step by step

  1. Compare the desired and actual position on the scan tool.
  2. Clean the throttle body with the key off, without forcing the throttle plate open.
  3. Run the relearn procedure.
  4. Check the connector.

How to fix the P0638 code

  • Clean the throttle body and run the relearn.
  • Replace the throttle body if the motor or the sensors fail.

Technical reference data

  • DC motor controlled by a PWM signal, with two position sensors.
  • Reference values: check the manufacturer data for your vehicle.

Brand-specific notes

This code is very frequent on several makes, and the cleaning and relearn steps matter on all of them.

P0638 on Volkswagen

Very common on Volkswagen.

P0638 on Audi

Very common on Audi.

P0638 on Nissan

Very common on Nissan.

P0638 on Ford

Very common on Ford.

P0638 on Toyota

Very common on Toyota.

Frequently asked questions about P0638

Can I drive with a P0638 code?
With caution. The vehicle can go into limp mode at any time, which means very little acceleration, so avoid busy roads until it is repaired.
Does cleaning fix it?
Many times, yes. Carbon around the throttle plate is the most common cause, and a proper cleaning often brings the throttle back to normal.
Do I have to run a relearn?
Yes, after you clean or replace the throttle body. The computer has to learn the throttle position again.
How much does it cost to fix P0638?
Between $0 and $600. A cleaning you do yourself is nearly free, and a new throttle body with installation is at the top of the range.
What does the P0638 code mean?
It is a generic OBD2 code that means the throttle actuator is not reaching the position the computer asks for on bank 1.
What is the most common cause of P0638?
For a P0638 code, the usual culprit is carbon buildup around the throttle plate. A worn motor or gears in the throttle body come next.

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Questions about the P0638 code

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