P0638: Throttle actuator control: range or performance (bank 1)
The electronic throttle is not moving the way the ECU expects. Usually carbon build-up in the throttle body, the plug or the motor itself.
| Code | P0638 |
|---|---|
| System | Engine and transmission |
| Group | P06xx, Control unit and auxiliary outputs |
| Type | Generic: it means the same on every make |
| Can you keep driving? | With care |
What P0638 means
On cars with an electronic accelerator, a small motor opens and closes the throttle valve that lets air in. This code means the actual throttle position is not following the position the ECU asks for. To protect itself, the car usually goes into limp mode with little power.
Most common causes
- Throttle body clogged with carbon that slows its movement
- Throttle body plug loose or corroded
- Throttle motor wires broken or chafed
- Low battery or unstable voltage
- Faulty throttle body (motor, gears or internal sensor)
Symptoms
- Engine warning light on
- Limp mode with very little power
- Unsteady idle or stalling
- Accelerator responds late or not at all
Can you drive with P0638?
With care The car usually goes into limp mode and barely accelerates, which can be risky when joining traffic. Only drive as far as the garage.
Open the bonnetthe in-depth explanation
How to check it
With the engine off, check whether the throttle body is heavily coated inside. On the scan tool, compare the desired and actual throttle position live as you press the pedal: they should move almost together.
How to read and clear P0638 with Final OBD
Plug an OBD2 scanner in under the steering wheel, switch the ignition on and open Final OBD. Under Faults you’ll see P0638 with its description and whether it’s confirmed, pending or permanent.
If the engine stores it over standard OBD, with FREE you read this code with its explanation for nothing and clear it. With PRO you also read the faults of every control unit and clear them in all of them.
Clearing the code only turns the light off: if the cause is still there, it comes back. Clear it once it’s fixed, and not right before an inspection. It’s all in how to read and clear fault codes and in inspections and OBD.
Similar codes
- P0634 The internal temperature of the engine or gearbox control unit is above normal
- P0635 The power steering control has an electrical fault
- P0636 The power steering control gives a lower signal than normal
- P0637 The power steering control gives a higher signal than normal
- P0639 The throttle actuator control (bank 2) gives readings outside the normal range
- P063A The generator voltage detection has an electrical fault
- P063B The generator voltage detection gives readings outside the normal range
- P063C The generator voltage detection gives a lower signal than normal
- P0600 Serial communication link fault
- P0601 Internal control module memory checksum error
- P0602 Control module programming error
- P0603 Internal control module keep alive memory (KAM) error
To understand it properly
We explain how that system works, with drawings and no waffle, in our mechanics guide: Accelerator.
What does code P0638 mean?
On cars with an electronic accelerator, a small motor opens and closes the throttle valve that lets air in. This code means the actual throttle position is not following the position the ECU asks for. To protect itself, the car usually goes into limp mode with little power.
Can you drive with P0638?
The car usually goes into limp mode and barely accelerates, which can be risky when joining traffic. Only drive as far as the garage.
How do you clear P0638?
With an OBD2 scanner and an app like Final OBD, which clears it for free if it’s stored by the engine control unit. But clearing it only turns the light off: if the cause isn’t fixed, P0638 comes back.
Read it on your car
Final OBD reads and clears engine faults through standard OBD for free, each one explained in plain English. With PRO it also reads the faults of every control unit, each make’s own codes included, and clears them in all of them.
