Worn or dirty throttle position sensor track inside the sensor housing; Corroded, loose, or damaged electrical connector at the throttle position sensor; Chafed or broken wires in the sensor's signal or reference circuit; Failed throttle position sensor internal electronics; Poor ground connection shared by the sensor circuit; Carbon buildup or mechanical binding on the throttle plate or shaft; Rarely, a faulty engine control module driver for the sensor circuit

DTC codes / P01xx · Fuel and air metering / P0120

P0120Throttle Position Sensor A Circuit Malfunction

Q: What does code P0120 mean?

Throttle Position Sensor A Circuit Malfunction. P0120 means the engine computer has detected a malfunction in the signal circuit for throttle position sensor A, which is the primary sensor that reports how far the throttle plate is open. The computer compares the sensor's voltage against expected values and flags the code when the reading is out of range, stuck, or inconsistent with other throttle data.

P0120 means the engine computer has detected a malfunction in the signal circuit for throttle position sensor A, which is the primary sensor that reports how far the throttle plate is open. The computer compares the sensor's voltage against expected values and flags the code when the reading is out of range, stuck, or inconsistent with other throttle data.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
Hesitation or stumble when accelerating from a stop
Reduced engine power or a limp-home mode
Poor fuel economy or erratic idle quality
Automatic transmission that shifts harshly or at the wrong time
A dead spot or surge in power during light throttle cruising

Common causes, most likely first

Worn or dirty throttle position sensor track inside the sensor housing
Corroded, loose, or damaged electrical connector at the throttle position sensor
Chafed or broken wires in the sensor's signal or reference circuit
Failed throttle position sensor internal electronics
Poor ground connection shared by the sensor circuit
Carbon buildup or mechanical binding on the throttle plate or shaft
Rarely, a faulty engine control module driver for the sensor circuit

How to diagnose and fix it

Scan all modules and record freeze-frame data to see the throttle angle and voltage at the moment the code set
Visually inspect the throttle position sensor connector and wiring for corrosion, looseness, or chafing
Back-probe the sensor signal wire and compare voltage to the manufacturer's specification through the full sweep of the throttle
Check the sensor reference voltage and ground circuit for correct values under load
Clean the throttle body and verify the throttle plate moves freely without binding
Replace the throttle position sensor if the signal is erratic or drops out during the sweep test
Clear the code and perform a throttle relearn or idle relearn procedure if required by the vehicle

Why a throttle position code is not always the sensor

A dirty throttle body can cause the sensor to report values outside the expected range even when the sensor itself is healthy, so cleaning the throttle plate often resolves the code without parts replacement.
Wiring harness chafing near the throttle body is a common hidden cause, and a wiggle test of the harness while watching live throttle data can reveal an intermittent signal that a static meter check misses.
Some vehicles set P0120 when the throttle position sensor signal does not agree with the accelerator pedal sensor or mass airflow sensor during a rationality check, so a fault in a related sensor can trigger this code.
A weak battery or poor ground can cause reference voltage to sag and set a false throttle position code, so checking charging system health before condemning the sensor is a smart first step.
After replacing the sensor, many vehicles require a throttle body calibration or idle relearn; skipping that step can leave the engine idling poorly and cause the code to return.

Can I keep driving with P0120?

You can usually drive the vehicle to a shop, but expect reduced power or limp-home mode and avoid heavy acceleration or highway merging until the fault is repaired. If the engine stalls or the throttle response becomes unpredictable, stop driving and arrange a tow.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.