CodeXOBD

P0120 — Throttle Pedal Position Sensor A Circuit Malfunction

P0120 means the module detected an electrical fault in the primary throttle position sensor circuit. A failed TPS, wiring damage, or a sticking throttle body is the usual cause.

Moderate

The engine may idle erratically, surge, or have dead spots in the throttle response. Some vehicles enter a reduced-power limp mode. This code will cause an emissions test failure.

$30–$300Parts, typical range
0.3–1.5 hLabour
estimateNot a quote · 2026 basis

What P0120 means

The throttle position sensor tells the module how far the throttle plate is open. Most modern vehicles use a dual-sensor design for redundancy — sensor A is the primary. P0120 sets when sensor A's signal is outside the expected range, either because the sensor has failed, the wiring is damaged, or the throttle body mechanical movement is restricted. This code often appears alongside idle or drivability complaints.

Technical summary
SystemPowertrain — fuel and air metering
How the fuel mixture is decidedAir passes the mass airflow sensor, then the throttle, into the intake manifold and the cylinder. The module injects fuel to match the measured air, and the upstream oxygen sensor reports the result so it can correct itself. Air entering after the sensor was never measured, which is why a leak downstream of it makes the mixture run lean.Air inAirflow sensormeasures massThrottleCylinderfuel added hereO₂ sensorreports resultAny air entering after the sensor is fuel the module never accounted for

Symptoms you may notice

What causes P0120

TPS sensor has failed

Very likelylow costeasy

The potentiometer inside the sensor wears or develops dead spots, producing erratic or out-of-range signals.

Wiring or connector fault

Likelylow costeasy

Chafed wires, corroded pins, or loose connectors in the TPS circuit can produce the same fault as a failed sensor.

Throttle body sticking or carbon buildup

Possiblelow costeasy

Carbon deposits can restrict throttle plate movement, causing the TPS to read outside its expected range at certain positions.

How to diagnose it

1

Monitor TPS voltage with live data

With the ignition on, watch the TPS voltage as you slowly open and close the throttle. It should sweep smoothly from approximately 0.5V closed to 4.5V wide open, with no dropouts or spikes.

Tools: OBD-II scanner with live dataExpected: Smooth 0.5-4.5V sweepIf it passes: Signal is smooth. The fault may be intermittent.If it fails: Dropouts, spikes, or stuck at one voltage — the sensor is faulty.
2

Inspect the throttle body

Remove the intake duct and inspect the throttle plate for carbon buildup or restriction. The plate should move freely through its full range.

Tools: Inspection light, Throttle body cleanerIf it passes: Throttle body is clean and moves freely. The sensor is the fault.If it fails: Clean the throttle body, clear the code, and re-test.
3

Check the TPS wiring and connector

Inspect the TPS connector for corrosion, loose pins, or damage. With the connector disconnected, check the 5V reference and ground wires for continuity back to the module.

Tools: Multimeter, Inspection lightIf it passes: Connector and wiring are intact. The sensor is confirmed faulty.If it fails: Repair the wiring or connector.

Related codes

P0121P0122P0123P0220

Common questions

Is P0120 the same as an electronic throttle problem?

It can be. On drive-by-wire vehicles, the TPS is part of the electronic throttle body. On cable-throttle vehicles, it is a separate sensor on the throttle shaft.

Last verified 2026-07-27 · Sources: SAE J2012 — Diagnostic Trouble Code Definitions and Failure Type Byte (SAE International)

This information is for general guidance and is not a substitute for professional diagnosis. Cost figures are estimates, not quotes.