Worn or faulty throttle position sensor, or throttle body or pedal sensor assembly (varies by model); Damaged wiring, chafed loom or open or short circuit in the sensor signal, reference or earth wires; Corroded, loose or contaminated connector terminals at the sensor or control unit; Dirty or carbon-fouled throttle body causing sticking or incorrect throttle angle readings; Throttle body motor or mechanical fault so actual position does not match the commanded position; Low or unstable sensor reference voltage caused by a fault elsewhere on the shared 5 V supply; Faulty engine control unit or an outdated calibration where the manufacturer has documented one.

P0120

Throttle/Pedal Position Sensor/Switch A Circuit.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
1: AreaFuel and air metering
20: FaultThe specific fault in that area

What it means

P0120 is the SAE J2012 generic code for a fault in the Throttle/Pedal Position Sensor/Switch 'A' circuit. The engine control unit monitors the sensor's signal voltage and sets the code when it falls outside the expected range, is erratic, or does not agree with other inputs such as the second sensor track, airflow or pedal position. Which physical sensor is 'A' depends on the vehicle, so check the model-specific information.

Symptoms

Malfunction indicator lamp on, often with an electronic throttle or engine warning lamp
Limp mode with reduced power and restricted throttle response
Poor or delayed acceleration, or hesitation when pulling away
Unstable, high or low idle, or stalling
Engine not revving above a set speed
Erratic or no response to the accelerator pedal

Possible causes

Worn or faulty throttle position sensor, or throttle body or pedal sensor assembly (varies by model)likely
Damaged wiring, chafed loom or open or short circuit in the sensor signal, reference or earth wireslikely
Corroded, loose or contaminated connector terminals at the sensor or control unitlikely
Dirty or carbon-fouled throttle body causing sticking or incorrect throttle angle readingspossible
Throttle body motor or mechanical fault so actual position does not match the commanded positionpossible
Low or unstable sensor reference voltage caused by a fault elsewhere on the shared 5 V supplypossible
Faulty engine control unit or an outdated calibration where the manufacturer has documented onerare

How to diagnose

Read all stored codes and freeze frame data, noting engine speed, load and throttle angle when the fault set, and check for related throttle, pedal or reference voltage codes
Visually inspect the throttle body, sensor, wiring and connectors for damage, chafing, water ingress, corrosion or loose fit
Check live data: with the ignition on, compare the throttle or pedal position values to the commanded values while slowly operating the pedal, looking for dropouts, jumps or disagreement between sensor tracks
Check the throttle body for carbon build-up or sticking and confirm the plate moves freely, following the manufacturer's procedure for your model
Measure the sensor reference voltage, earth and signal at the connector against the manufacturer's specification
Wiggle-test the harness and connector with live data displayed to find intermittent faults, and check continuity and resistance of each wire to the control unit
Check the battery condition and charging voltage, as low voltage can upset the sensor readings
Look for relevant technical service information for your model, including any throttle relearn or adaptation requirement after repair

How to fix

Repair or replace damaged wiring and terminals, ensuring proper insulation and routing
Clean and secure connectors, replacing any with corroded or loose terminals
Clean the throttle body using a suitable method for the model, then perform the throttle adaptation or relearn
Replace the faulty throttle position sensor, throttle body assembly or pedal sensor assembly as specified for the vehicle, then carry out any required relearn
Rectify any fault on the shared reference supply that is affecting the sensor
Update or replace the control unit only if testing confirms it faulty or a documented calibration issue applies

Can I keep driving?

Medium severity

The car may be driven carefully a short distance if it runs normally, but it can drop into limp mode or stall without warning, which is unsafe in traffic. Get it diagnosed soon and avoid driving if power is erratic or the engine stalls.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.