Faulty throttle position sensor or pedal position sensor (worn track or internal fault); Open circuit in the sensor ground or reference wire, causing the signal to read high; Signal wire shorted to the 5 V reference or to battery voltage; Damaged, corroded or loose connector terminals at the sensor or control unit; Faulty or dirty electronic throttle body (on drive-by-wire systems the sensor is often part of the throttle body); Internal fault in the engine control unit or its sensor supply.

P0123

Throttle/Pedal Position Sensor/Switch A Circuit High.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
1: AreaFuel and air metering
23: FaultThe specific fault in that area

What it means

P0123 means the engine control unit has seen the signal voltage from throttle position sensor or pedal position sensor 'A' sit higher than the expected range. This usually points to a short to voltage, an open circuit on the signal or ground wire, or a faulty sensor. The control unit often limits engine power as a protective measure when it cannot trust the throttle or pedal reading.

Symptoms

Engine warning light on
Limited power or limp-home mode
Poor or erratic throttle response
High or unstable idle, or engine stalling
Hesitation or surging when accelerating
Cruise control not working

Possible causes

Faulty throttle position sensor or pedal position sensor (worn track or internal fault)likely
Open circuit in the sensor ground or reference wire, causing the signal to read highlikely
Signal wire shorted to the 5 V reference or to battery voltagepossible
Damaged, corroded or loose connector terminals at the sensor or control unitpossible
Faulty or dirty electronic throttle body (on drive-by-wire systems the sensor is often part of the throttle body)possible
Internal fault in the engine control unit or its sensor supplyrare

How to diagnose

Read all stored codes and freeze frame data to see engine load, throttle angle and conditions when the code set, and note any other sensor supply or throttle codes.
Check live data: with ignition on and engine off, compare throttle and pedal position readings at rest and fully pressed, looking for a reading stuck high or jumping.
Inspect the wiring and connectors at the throttle body and pedal for damage, chafing, water ingress, corrosion or pushed-out pins.
Check whether sensor A and sensor B (where fitted) track each other smoothly; a mismatch helps identify which sensor or circuit is at fault.
Using the manufacturer's wiring diagram for the model, test the 5 V reference, ground and signal circuits at the sensor connector for opens or shorts to voltage.
Wiggle the harness while watching live data to find intermittent faults.
Inspect the throttle body for heavy carbon build-up or a sticking plate, as procedures vary by engine.
If wiring and supply are good, test or substitute the suspect sensor or throttle body, then perform any throttle adaptation or relearn the model requires.

How to fix

Replace the faulty throttle position sensor, pedal assembly or throttle body as the diagnosis shows.
Repair open circuits or shorts in the reference, ground or signal wiring.
Clean, repair or replace damaged connectors and terminals.
Clean the throttle body if contamination is affecting movement, following the manufacturer's method.
Carry out the throttle adaptation or relearn procedure after the repair, then clear the code and road test to confirm it does not return.

Can I keep driving?

Medium severity

The car may be driveable in limp-home mode, but power and throttle response can be unpredictable, so avoid it where possible. Get it checked soon, as sudden loss of power or stalling can be unsafe in traffic.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.