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Powertrain fault code

P0121: Throttle/Pedal Position Sensor/Switch "A" Circuit Range/Performance

Fix soon

Usually safe to drive gently to a workshop, but fuel use and running can suffer. Have it checked soon.

What P0121 means

The engine computer is getting a reading from the throttle or pedal position sensor that is missing, out of range or doesn't make sense. The throttle or pedal position sensor reports how far the throttle is open.

Common causes

  • Faulty throttle position sensor or throttle body
  • Dirty throttle body
  • Damaged wiring or connector

What to check first

  1. Scan the car to confirm the code and see if others are stored with it.
  2. Check the sensor plug and wiring for corrosion, damage or a loose connection.
  3. Compare the live sensor reading with a known-good value before replacing the part.

Get P0121 explained for your car: $2.99

  • P0121 explained in full for your make and model: meaning, how urgent, likely causes and what to check, in order.
  • A short personal note from us within 24 hours, or your money back.
  • Your own private report page you can save as a PDF or show your mechanic.

Read your car's codes yourself, free

Plug a cheap ELM327 OBD-II adapter into the port under the dashboard and open the scan tool: Chrome or Edge on a computer with a USB adapter, or Chrome on Android with a Bluetooth LE adapter. It reads and clears codes and shows emissions readiness. It does not work on iPhone.

Open the free scan tool

Need help with P0121?

Tell us your car and what it is doing with P0121. We reply by email with what to check first, in plain words. Free.

Related codes

P0120P0122P0123

General guidance only, not a diagnosis. A qualified mechanic should confirm the cause before you replace parts.