P0120 Throttle/Pedal Position Sensor/Switch A Circuit Malfunction

P0120 points to a throttle or pedal position sensor/switch A circuit malfunction. The module sees an electrical fault or implausible signal in the throttle-position path.

Code details

Generic OBD-II · P0

System: Fuel / Air
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not clean or replace the throttle body before checking redundant sensor correlation and wiring integrity.

Symptoms of P0120

Check-engine light on, sometimes with rough or uneven running.
Hesitation, surging, or a noticeable change in fuel economy.
Occasionally hard starting or a smell of unburnt fuel.

Common causes of P0120

A failing or contaminated sensor (MAF, MAP, oxygen or air-fuel sensor).
Intake or vacuum leaks, or an exhaust leak near an upstream sensor.
Wiring, connector, or fuel-delivery problems that skew the reading.

Useful checks before replacing parts

Compare throttle position A with redundant throttle or pedal channels while slowly opening the throttle.
Inspect connector fit, terminal tension, reference voltage, sensor ground, and harness routing near the throttle body.
Check for throttle-body contamination, binding, or related electronic throttle control codes.

Related OBD-II codes

These nearby fuel / air entries can help compare wording and pin down the fault area.