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

On vehicles with electronic throttle control, the throttle (ETC) actuator controls the engine’s air intake. It makes sure that the right amount of air enters the engine to mix with the fuel for efficient energy production. Too much air will result in a lean fuel-air mixture, while too little air leads to the engine running rich.

The powertrain control module (PCM) monitors the throttle actuator’s movement. It will log a P0638 code if it detects that the actuator is not in the position it should be in.

What Does the P0638 Code Mean?

Diagnostic trouble code (DTC) P0638 stands for “Throttle Actuator Control Range/Performance.”

The throttle actuator is a modern version of the throttle body, a device at the inlet of the intake manifold with a butterfly valve inside it. In a drive-by-wire system, the actuator is fully computerized and dispenses with physical cables.

The throttle actuator typically has two throttle position sensors. The throttle position sensor keeps the PCM informed about the throttle actuator being open. The throttle position sensors, together with one or more accelerator pedal sensors, provide the PCM with information regarding the desired and actual throttle position.

The PCM uses the information to adjust how much fuel the injectors spray, among other things. If it doesn’t get the right response from the actuator, it will set the powertrain code P0638.

Note: The definition of code P0638 can differ according to the vehicle manufacturer. Check the appropriate repair manual or repair database for the exact code definition.

What are the Common Causes of the P0638 Code?

• Faulty throttle body assembly
• Bad throttle position sensor
• Wiring problems
• Bad PCM

What are the Common Symptoms of the P0638 Code?

• Illuminated check engine light
• Engine performance problems, such as rough running and stalling
• Vehicle stuck in “limp” mode

How to Diagnose the P0638 Code

The P0638 code is a generic trouble code, which means vehicles made by different auto manufacturers can log it. The affected vehicles can exhibit similar symptoms, but that doesn’t mean that they share the same steps for diagnosing the code. The process can vary depending on the make and model.

If you’re not confident about conducting diagnostic tests on your vehicle, it’s a good idea to bring it to a professional mechanic. Otherwise, you can go ahead and diagnose the issue yourself. To help you get started, here are some videos that can give you an idea of what the process might involve:

How to Fix the P0638 Code

Fixing the P0638 code can be tricky, especially if you don’t have the right tools and know-how. So if you’re not confident that you can do it yourself, take your vehicle to an auto repair shop and let professionals resolve the issue.

But if you’re a DIYer with in-depth automotive know-how, you can go ahead and resolve the P0638 code on your own. Consult a vehicle-specific repair manual or online repair database before you get started.