EngineLightCodes
Powertrain code

P0120 Throttle/Pedal Position Sensor/Switch A Circuit

Severity
Fix soon
Typical repair cost
$30–$500
Do it yourself
Possible, medium
Shop time
0.5–2 hours

Sensor A is, in practice, throttle position sensor 1 at the throttle body; the accelerator pedal has its own codes (P2120 onwards).

How the engine computer detects it

With a cable-operated throttle there is a single potentiometer (about 0.5 V closed to 4.5 V wide open). Electronic throttles have two sensors sharing a 5 V reference and ground, usually running in opposite directions – on GM throttle sensor 1 falls from 3–4 V at idle to below 1 V at full throttle. P0120 is the general circuit fault, used when the fault cannot be classed as low or high or when the sensor is digital. Ford sets it on digital SENT throttle sensors when the sensor reports an error for more than 4 s, together with the MIL and wrench lamp; Saab Trionic used it as a collective code. GM and Ford's analogue throttles report P0122/P0123 instead. Electronic throttles then fall back to a spring-loaded limp position with limited power.

Written from public technical sources and not yet checked by a mechanic. How we write these pages

Symptoms

  • Check engine light, on electronic throttles also wrench lamp
  • Limp mode with reduced power ('Reduced Engine Power') on electronic throttles
  • Raised or unsteady idle (cable systems)
  • Poor throttle response, jerky driving

Common causes

  1. Connector at the throttle body corroded or loose, broken wire Most likely
  2. Sensor or throttle body with integrated sensor faulty Possible
  3. 5 V reference disturbed (short on another sensor of the same circuit) Possible
  4. Engine control module faulty Less likely

How to diagnose P0120

  1. Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
  2. Inspect the parts involved: throttle position sensor, throttle body, sensor wiring, sensor reference voltage.
  3. Work through the causes above from most to least likely, cheapest checks first.
  4. Clear the code and drive a full drive cycle to confirm the repair held.

Reading the code

P
Powertrain
0
Generic (SAE) code
1
Fuel and air metering
20
Specific fault

Questions drivers ask

Can I drive with code P0120?

Drive gently and only as far as you need to. The engine computer may limit power to protect the engine, so avoid highways and heavy traffic until it's fixed. If the check engine light starts flashing, pull over.

Will my car pass an emissions inspection with P0120?

Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.

Can I fix P0120 myself?

Often yes, with an OBD-II scanner and basic tools. Difficulty: medium. Start with the cheapest checks before replacing expensive parts.

Often reported together

Codes that owners mention in the same NHTSA complaints as P0120. They can point to a shared cause, so it's worth checking them together.

This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.