P0638: Throttle Actuator Control Range/Performance — Bank 1
What to do
Expect severely reduced power — often barely enough to move, and the throttle may feel unresponsive. This is deliberate protection rather than an additional fault. It is safe to drive slowly to somewhere it can be looked at, but do not plan a journey; the power limit is not something you can work around.
What this code means
The electronic throttle is not reaching the position commanded on bank 1. On a drive-by-wire engine there is no cable — the pedal is a sensor, the throttle is a motor, and the module closes the loop between them. When the loop cannot be closed, the module restricts the engine severely.
That restriction is not a malfunction; it is the design. A throttle that does not go where it is told is the one fault a modern engine will not tolerate, so the vehicle drops to a heavily limited power mode that gives just enough to move.
Carbon around the throttle plate is the most common cause and cleaning is a genuine repair. A worn throttle position sensor, a failing motor or a damaged connector account for most of the rest.
Likely causes
Start here
- Carbon deposits in the throttle body · easy
- Faulty throttle position sensor · moderate
- Faulty throttle actuator motor · moderate
- Corroded or loose connector · easy
Less common
- Binding throttle plate or linkage · moderate
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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