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P0638 OBD-II Trouble Code: Throttle Actuator Control Range/Performance (Bank 1)

Check Engine Light

P0638 code definition

This diagnostic power train code represents a problem happening with the vehicle’s throttle actuator control range in bank one.

What the P0638 code means

In many newer model vehicles, the throttle body is hooked up to a drive by wire system. This controls the throttle body through a sensor on the automobile’s gas pedal, an electric actuator motor that’s inside the throttle body and the Powertrain Control Module (PCM) or Engine Control Module (ECM).

This PCM/ECM leverages the throttle position sensor (TPS) to keep track of the actual throttle blade position on the vehicle as well as when the position is no longer in range of the target range. If it picks up that the throttle blade position is no longer in range, the P0638 code will show on the scanner. Bank one refers to the location of cylinder number one on the engine. Usually, though, you’ll get a code that simply signifies a problem with any of the cylinders as one throttle body covers all of them.

That being said, if the vehicle does have this type of throttle body, there’s little you can do to fix a problem similar to P0638. The majority of the time, your only option will be to simply replace it. In the event of a motor failure, these engines are designed to be held open thanks to their spring actuation. In some cases, though, like when a complete failure occurs, the throttle will be totally unresponsive and the vehicle will only move at extremely slow speeds.

What causes the P0638 code?

There are a number of potential causes that could trigger the P0638 trouble code. The most common versions would be:

  • A malfunctioning pedal position sensor
  • A malfunctioning throttle position sensor
  • A malfunctioning throttle actuator motor
  • The throttle body is dirty
  • The connection is loose or dirty
  • The wiring harness is loose or dirty

As you can see, many of these problems can be addressed through fairly simple means. A lot of times, it just takes a bit of cleaning. However, if you go through the above potential causes and none of them seem to be behind it, keep in mind that the problem could also be that the PCM/ECM has malfunctioned.

What are the symptoms of the P0638 code?

There are really only two main symptoms associated with the P0638 code:

  • The vehicle may hesitate to accelerate when you put the pedal down
  • The check engine light is on

Obviously, you may notice both too. With the throttle open, you should definitely notice a problem with trying to accelerate, whether the check engine light comes on or not.

How does a mechanic diagnose the P0638 code?

To diagnose the problem causing the P0638 code, do the following:

  • Hook up your OBD-II scanner and download the freeze frame data for your customer’s car. Make sure you look at any other trouble codes that may have been stored in the vehicle’s PCM. In some cases, you will need to resolve these before you fix the throttle problems.
  • Even if the customer swears they are having throttle problems, take it for a quick test drive to see for yourself. If the problem was a temporary issue, the code may still be stored despite the throttle working fine.
  • Finally, inspect the throttle body to look for signs of problems with the connection, wire, systems, etc.

Common mistakes when diagnosing the P0638 code

Not taking the vehicle for a test drive is definitely a mistake. If you don’t notice anything, the PCM may be acting up. However, you also want to carry out a full inspection just in case. Check for a faulty cylinder or problems with the fuel injector.

How serious is the P0638 code?

This is a pretty serious problem. For one thing, until the underlying problem is fixed, there’s always the possibility that the vehicle won’t start. Far worse, though, is the fact that the automobile may become difficult to drive while it’s already on the road.

What repairs can fix the P0638 code?

Try the following:

  • Clean out the throttle body
  • Replace any bad connections
  • Fix the wire system

Additional comments for consideration regarding the P0638 code

Although poor acceleration may not seem like it needs to be a huge priority, this is a problem that could cause a crash, so it’s best to address ASAP.

Need help with a P0638 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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