P0123: Throttle/Pedal Position Sensor/Switch "A" Circuit High
The throttle position sensor A signal is above its normal range.
High risk
Drivable with care, but power is often limited. Have it checked soon.
Short answer · Can I keep driving with P0123?
Usually only gently, as power may be limited. Have the sensor and wiring checked soon.
What does P0123 mean?
Code P0123 means the signal from throttle position sensor A is higher than a working sensor gives. Common causes are a short to voltage, a poor sensor ground or a faulty sensor.
What the car does when the code is set
The check engine light comes on, and on many cars an electronic throttle warning too. The engine often goes into a reduced-power mode: it responds slowly to the pedal and may only run at a fixed, higher idle speed.
How the system works
The throttle position sensor tells the engine control unit how far the throttle plate is open. On modern cars with drive-by-wire, there is no cable: the accelerator pedal has its own sensors and a motor opens the throttle. Both pedal and throttle use two sensor signals that must always agree. If one signal is out of range or the two do not match, the control unit cannot trust it and limits power for safety.
Common symptoms
Possible causes
Listed without ranking. The cause on your car depends on make, engine and mileage — see the maker notes below.
- Dirty or sticking throttle bodyCarbon around the throttle plate can stop it from moving as commanded.
- Worn or faulty position sensorThe sensor track wears, giving jumps or dropouts in the signal.
- Wiring or connector faultCorrosion, loose pins or chafed wires disturb the sensor signals.
- Accelerator pedal sensor faultOn drive-by-wire cars, a faulty pedal sensor can set related codes.
- Low battery voltageUnstable supply voltage can upset the electronic throttle.
How it is diagnosed
- Note the warning lights and powerMany cars go into a reduced-power mode with this fault. Note whether the engine responds normally to the pedal.
- Inspect the connector and wiringCheck the throttle body and pedal sensor connectors for corrosion, damage and loose pins.
- Clean the throttle body if dirtyUse a suitable cleaner with the ignition off, and follow the maker's procedure; many throttles need a relearn afterwards.
- Check sensor signals with a scan toolA workshop compares both sensor signals while the pedal or throttle moves slowly.Keep fingers away from the throttle plate; on electronic throttles it can move when the ignition is switched on.
Questions about P0123
Is P0123 dangerous?
It is not usually dangerous in itself, but sudden power loss in traffic can be. Drive carefully and have it fixed soon.
Why does my car only drive slowly with this code?
Throttle faults affect how the engine responds to the pedal, so the control unit limits power as a safety measure until the fault is fixed.