A faulty throttle position sensor (TPS) that has worn out internally and no longer produces the correct voltage sweep.; Damaged or corroded wiring between the TPS and the engine computer, including a broken wire or a poor ground connection.; A short to ground on the signal circuit, often caused by chafed insulation where the harness rubs against a metal bracket.; Loose or dirty electrical connectors at the TPS or at the computer, leading to intermittent low signal voltage.; A misadjusted or improperly installed TPS that is not sitting at the correct angle on the throttle shaft.; Rarely, a failed engine computer driver circuit that cannot read the sensor signal correctly.

DTC codes / P01xx · Fuel and air metering / P0122

P0122Throttle Position Sensor A Circuit Low Input

Q: What does code P0122 mean?

Throttle Position Sensor A Circuit Low Input. P0122 means the engine computer has detected that the signal voltage from throttle position sensor A is lower than it should be for the current throttle position. The computer expects the sensor's output to rise as the throttle opens, and a sustained low reading indicates an open circuit, a short to ground, or a failed sensor.

P0122 means the engine computer has detected that the signal voltage from throttle position sensor A is lower than it should be for the current throttle position. The computer expects the sensor's output to rise as the throttle opens, and a sustained low reading indicates an open circuit, a short to ground, or a failed sensor.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

The check engine light is illuminated, often with no other noticeable symptoms.
The engine may idle poorly, stumble, or stall when you come to a stop.
Acceleration may feel flat or delayed because the computer is not receiving an accurate throttle opening signal.
An automatic transmission may shift harshly or at the wrong time due to incorrect throttle position data.
The vehicle may enter limp mode, limiting engine speed and power to protect the drivetrain.

Common causes, most likely first

A faulty throttle position sensor (TPS) that has worn out internally and no longer produces the correct voltage sweep.
Damaged or corroded wiring between the TPS and the engine computer, including a broken wire or a poor ground connection.
A short to ground on the signal circuit, often caused by chafed insulation where the harness rubs against a metal bracket.
Loose or dirty electrical connectors at the TPS or at the computer, leading to intermittent low signal voltage.
A misadjusted or improperly installed TPS that is not sitting at the correct angle on the throttle shaft.
Rarely, a failed engine computer driver circuit that cannot read the sensor signal correctly.

How to diagnose and fix it

Connect an OBD-II scan tool and read live throttle position data while slowly opening the throttle by hand to confirm the signal stays low or drops out.
Visually inspect the TPS connector and wiring for corrosion, loose pins, or chafed insulation, and repair any damage found.
Back-probe the TPS signal wire with a multimeter and measure voltage with the key on and throttle closed, then compare to the manufacturer's specification.
Check the sensor's ground circuit for excessive resistance using a voltage drop test rather than a simple continuity check.
If the wiring and ground are good but the signal voltage does not change smoothly, replace the throttle position sensor and clear the code.
After any repair, clear the adaptive memory and perform a throttle relearn procedure if the manufacturer requires it, then verify the code does not return.

What a low TPS signal really tells you

A P0122 can be set by a perfectly good TPS if the reference voltage feed to the sensor is low, so always check the 5-volt reference circuit before condemning the sensor.
Many technicians replace the TPS only to find the real fault is a worn spot in the harness where it passes near the exhaust or a sharp bracket, so a wiggle test while watching live data is essential.
On some vehicles, a low TPS signal can be caused by a failing accelerator pedal position sensor on drive-by-wire systems, even though the code names the throttle position sensor.
The code does not always mean the sensor is dead; a loose battery ground or a poor engine ground can pull the signal voltage down and set P0122 intermittently.
If the TPS signal is low only when the engine is hot, suspect a failing sensor that breaks down with heat rather than a wiring fault, and test it cold and hot.

Can I keep driving with P0122?

You can usually drive the vehicle to a repair shop, but avoid heavy acceleration and towing because the computer may be using a default throttle value that limits power. If the engine stalls repeatedly or enters limp mode, stop driving and have it towed.

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.