Draft guidance: awaiting Claude spot-check, qualified-mechanic review and named-editor approval. Do not use a fault code alone to replace parts.

P0120: Throttle/pedal position sensor or switch “A” circuit

The engine computer has detected an electrical fault in throttle or accelerator-position circuit “A”.

What P0120 means

The engine computer has detected an electrical fault in throttle or accelerator-position circuit “A”. Depending on the vehicle, “A” may be one track inside the electronic throttle body or another position-sensing channel. Vehicle-specific wiring information is needed before deciding which component is involved.

Can I still drive?

This fault can produce reduced-power mode or an unpredictable accelerator response. Arrange recovery if the vehicle hesitates badly, surges, stalls, fails to respond normally to the pedal, displays a reduced-power warning or cannot keep pace safely. If there is only a steady amber warning and throttle response is completely normal, limit driving to a cautious trip directly to a garage; avoid motorways, overtaking and dense traffic.

Symptoms

• Engine-management or reduced-power warning.
• Delayed, weak or absent acceleration.
• Limp-home mode.
• Hesitation, jolting or surging.
• Rough idle, stalling or difficult starting.
• Increased fuel consumption.

Common causes

• Failed throttle-position or accelerator-position sensor.
• Worn internal sensor track.
• Fault within an integrated electronic throttle body.
• Loose, wet or corroded connector.
• Damage to the signal, 5-volt reference or earth wiring.
• Chafed harness; control-unit fault rarely.

Safe first checks

• Record stored and pending codes plus freeze-frame data before clearing them. With the ignition off, inspect accessible throttle-body and pedal connectors and the nearby loom for looseness, water, corrosion or rubbing. Check that the intake hose is secure and that no floor mat obstructs the pedal. A suitable scan tool can display position data while the vehicle is stationary, but do not force a motorised throttle plate or probe reference-voltage circuits without the correct procedure.

Typical UK fix cost

Approximately £100–£500. The lower end allows for diagnosis and a straightforward connector, wiring or separately replaceable sensor repair; the upper end allows for an integrated throttle-body assembly and adaptation. Unusual access, premium components or extensive electrical diagnosis can exceed this range.

Related models

This is a generic OBD-II code used across many makes and models. The exact test thresholds, component layout and repair route vary by engine and manufacturer, so check vehicle-specific technical information before ordering parts.

Related fault codes

• P0117: Engine coolant temperature circuit low input
• P0118: Engine coolant temperature circuit high input
• P0121: Throttle/pedal position sensor or switch “A” range/performance
• P0122: Throttle/pedal position sensor or switch “A” circuit low

Sources

• Toyota service information — P0120/P0123 throttle circuit diagnostics
• HELLA Tech World — throttle potentiometer function and testing
• Fixter — UK throttle-body replacement cost guide
• GOV.UK MOT manual — engine malfunction indicator classification

A diagnostic trouble code identifies a system or circuit to investigate. It does not prove that a named part has failed. Preserve freeze-frame data and seek a vehicle-specific diagnosis before clearing the code.