CHECK ENGINE LIGHT CODE

P0120: Throttle/Pedal Position Sensor/Switch "A" Circuit

The engine computer sees a problem in the signal from throttle or pedal position sensor A, which tells it how far you are pressing the gas.

SeriousDrive only if the car responds normally, and go straight to a shop. Many cars go into reduced power mode with this code, which can be unsafe in traffic.

What P0120 means

The throttle position sensor reports how far the throttle plate is open, and on newer cars the pedal position sensor reports how far your foot is pressing the gas. Both send a voltage that rises smoothly as you press down. The engine computer uses those signals for fuel, spark timing and, on drive-by-wire cars, to actually open the throttle with a motor. P0120 is a general circuit fault for sensor A, meaning the signal is missing, erratic or electrically wrong. Because throttle control is a safety system, many vehicles respond by limiting power, which RepairPal and KBB both treat as a serious condition. Common causes are a worn sensor, carbon in the throttle body, and wiring or connector problems. Shops use a scan tool to watch the sensor voltage sweep as the pedal moves, looking for dropouts, and check the 5 volt reference and ground. On many modern cars the sensor is part of the throttle body, so the fix may mean replacing that whole unit.

Common symptoms

Check engine light, sometimes a wrench or reduced power light
Hesitation or surging on acceleration
Erratic or high idle
Engine stalling
Car limited to low power (limp mode)

Most common causes

Faulty throttle position sensor
Worn accelerator pedal position sensor
Damaged wiring or corroded connector
Dirty or carbon-filled throttle body
Bad 5 volt reference or ground circuit

What to check yourself first

Check the throttle body connector and the accelerator pedal connector for corrosion or loose fit. Look inside the throttle body for heavy carbon buildup. Make sure a floor mat is not pressing on or jamming the gas pedal.

Typical fixes and what they cost

Fix	Typical cost	Note
Replace throttle position sensor	$185-$258	On older cable throttle cars the sensor is separate and replaced on its own.
Replace throttle body	$623-$766	On drive-by-wire cars the sensor is usually built into the electronic throttle body.
Electrical diagnosis to find a wiring or connector fault	$122-$179	For chafed wiring or a bad connector, a common reason sensors are replaced for nothing.

Typical US price ranges for parts and labor, not quotes. Your shop should confirm the cause with a diagnostic before replacing parts.

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