P2100: Throttle Actuator A Control Motor Circuit/Open
Do not keep driving
Expect the engine to run but refuse to rev much above idle — that is the throttle sitting on its spring default, which is deliberate. The car is not really driveable in traffic; have it recovered rather than trying to get home on a fast idle.
What this code means
A circuit fault in the motor that opens and closes the throttle plate. On a drive-by-wire vehicle — which is nearly all of them now — this motor is the connection between the accelerator pedal and the engine. There is no cable.
That single fact governs the whole of the P21xx range. The pedal is a pair of sensors, the throttle is a motor with its own pair of sensors, and a module in between decides what one should do about the other. It brings real benefits — traction control, cruise control, stability intervention and idle control all become software rather than extra hardware — and it brings one obligation: the system must be able to fail safely, because a throttle with a mind of its own is not an acceptable outcome.
The throttle plate is therefore spring-loaded to a default position slightly open, so that if the motor loses power the engine keeps running at a fast idle rather than stopping dead. Enough to limp, not enough to accelerate. When you meet the phrase "limp home" on a modern petrol engine, this spring is usually what is doing the limping.
With the motor circuit open, that is exactly where the throttle goes.
Likely causes
Start here
- Faulty throttle actuator motor · moderate
- Open circuit in throttle motor wiring · moderate
- Corroded or loose connector · easy
Less common
Rare
- Faulty engine control module · specialist
Symptoms
Components involved
Information, not instruction
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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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