Engine

P0120 — Throttle/Pedal Position Sensor "A" Circuit Malfunction

Severity: medium Drive with care, to a shop

What P0120 means

The engine control unit constantly compares the throttle or accelerator pedal position sensor signal against an expected voltage range. P0120 sets when that signal is out of range, missing or does not agree with other inputs. Common triggers are a failed sensor, wiring damage or a poor connector contact. Without a reliable signal, the ECU cannot tell how far the driver is pressing the pedal.

Symptoms

  • Check Engine Light on
  • Rough or surging idle
  • Hesitation when accelerating
  • Reduced power or limp mode
  • Possible stalling
  • Sluggish throttle response

Possible causes

  1. Failed throttle position sensor (TPS)
  2. Damaged or corroded wiring and connectors in the sensor circuit
  3. Faulty accelerator pedal position (APP) sensor
  4. Dirty throttle body interfering with the throttle plate
  5. Throttle relearn not performed after cleaning or replacement
  6. Rarely, an ECU fault or software issue

How to diagnose

  1. Scan for codes and freeze frame data, and note any other throttle or pedal codes
  2. Inspect the wiring and connectors at the throttle body and pedal for chafing, corrosion or loose pins
  3. Watch live data: the sensor signal should change smoothly with pedal movement, with no spikes or dropouts
  4. Use a multimeter to check the 5 V reference, ground and signal wire at the sensor
  5. Compare pedal sensor and throttle sensor readings; they should track each other
  6. Inspect the throttle body, clean it if dirty and confirm the plate moves freely
  7. Test the circuit wires for opens and shorts to ground or voltage
  8. After repair, clear the code and perform a throttle relearn

Common fixes

  • Repair wiring or replace damaged connectors
  • Replace the throttle position sensor or the whole throttle body assembly
  • Replace the accelerator pedal position sensor
  • Clean the throttle body and perform a relearn
  • Reflash or replace the ECU only after everything else is ruled out

P0120 on different brands

Ford · manuals
On Ford, P0120:01 is documented for the 2024-2025 gasoline OBD monitor strategy and identifies the detected monitor condition in the sensor circuit rather than proving a specific part has failed.

Questions and answers

Can I drive with a P0120 code?

Briefly and carefully, yes, but the engine may enter limp mode or stall. Have it diagnosed soon.

What most often causes P0120?

Usually a worn throttle position sensor or a poor connection in the wiring or connector. The pedal sensor and throttle body cleanliness are also worth checking.

Will cleaning the throttle body fix P0120?

Sometimes, if dirt is the cause. Clear the code and do a throttle relearn afterward, or the idle may stay unstable.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.