P2120: Throttle/Pedal Position Sensor/Switch D Circuit
Do not keep driving
Expect the engine to run but refuse to respond to the accelerator properly, or to drop into reduced power. Ask for the pedal connector in the footwell to be inspected before the pedal assembly is quoted — that footwell gets wet, corrosion there is common, and the sensors usually only come as part of a complete pedal.
What this code means
A circuit fault in position sensor D. On most vehicles sensors D and beyond belong to the accelerator pedal rather than the throttle, and knowing which end of the system a code refers to is the first thing to establish, because the two live in completely different environments and fail for completely different reasons.
The throttle sits in the engine bay and fails from heat and carbon. The pedal sits in the footwell — which is, on any honest assessment, one of the wettest and most abused parts of the vehicle. Wet shoes drain into it, drinks get spilled into it, floor mats trap moisture against the carpet beneath, and the sensor's connector is down there in the middle of it. Corrosion in a pedal connector is a leading cause of these codes and it is found by looking rather than by testing.
The other thing worth knowing before parts are priced: the sensors are integral to the pedal assembly on nearly every design. "Replace the pedal sensor" means replacing the whole pedal, and it is not a trivial part — which makes checking the connector first worth real money.
Likely causes
Start here
- Corroded accelerator pedal connector · easy
- Faulty accelerator pedal position sensor · easy
- Water ingress into the footwell · moderate
Less common
- Open circuit in sensor wiring · moderate
- Failed sensor reference voltage supply · moderate
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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- The car — make, model, year and engine. The same fault behaves differently on each.
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