P0120: Throttle/Pedal Position Sensor/Switch A Circuit

What does P0120 mean?

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

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

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

• High Connector at the throttle body corroded or loose, broken wire
• Medium Sensor or throttle body with integrated sensor faulty
• Medium 5 V reference disturbed (short on another sensor of the same circuit)
• Low Engine control module faulty

Likelihood is a general estimate across vehicles; your make and model may differ.