What does P0121 mean?

Throttle/pedal sensor A gives a reading that does not match what the ECU expects.

Can a dirty throttle body cause P0121?

Yes. Carbon build-up can make the throttle stick and produce an irregular signal.

Engine sensors

P0121 — Throttle/Pedal Position Sensor/Switch A Circuit Range/Performance

The throttle position sensor (or accelerator pedal sensor) A reading does not agree with the expected value or with the second sensor. The ECU may limit engine power to protect the engine.

Severity: Medium

Common causes

Worn or dirty throttle position sensor
Dirty throttle body or sticking throttle plate
Faulty accelerator pedal sensor
Damaged wiring or connector
Faulty throttle actuator motor

Symptoms

Hesitation or surging
Rough or unstable idle
Reduced power or limp mode
Check engine light

How to check

Clean the throttle body and check the plate moves freely
Compare the two throttle/pedal sensor signals on a scan tool while moving slowly
Check wiring and connectors
Replace the sensor or throttle body if the signals stay out of agreement

Can you keep driving?

Take care: the car may enter limp mode with reduced power. Avoid driving in dangerous traffic until it is checked.

Frequently asked questions

What does P0121 mean?: Throttle/pedal sensor A gives a reading that does not match what the ECU expects.
Can a dirty throttle body cause P0121?: Yes. Carbon build-up can make the throttle stick and produce an irregular signal.

General reference information. It does not replace a diagnosis on your own vehicle. The same code can have different causes depending on make, model year and engine; check the manufacturer's documentation or ask a technician with a scan tool.