Fault codeP0123

MODERATE

Throttle/Pedal Position Sensor/Switch A Circuit High Input

What this code means

Throttle/Pedal Position Sensor/Switch A Circuit High Input.

P0123 is a generic code: it means the same thing on every make. P0123 belongs to family P01xx — Fuel and air metering. Its page explains how to read a code and groups all its codes by part.

Type of fault

The control unit reads a voltage on this circuit above its expected range. Usual causes: a broken wire or a poor ground, a short to a supply voltage, or the component itself. As with a low signal, check the wiring and connector before the part.

Throttle and accelerator pedal position sensors

On modern cars there is no cable between the pedal and the engine: sensors in the accelerator pedal tell the control unit how far you press, and an electric motor opens the throttle, whose position is measured by two more sensors. Each position is measured twice for safety, and both signals must agree.

What you notice

The engine often goes into limp mode: idle speed or very limited power, the accelerator barely responding. Sometimes jerks or idle speed surges.

How to check it

Check the connectors on the pedal and on the throttle body. A dirty throttle body can disturb the readings: cleaning it, then a relearn procedure, fixes some cases. Klaro shows the throttle and pedal positions; pressing the pedal slowly, they should rise smoothly without jumps.

Watch it live in Klaro

With an OBD2 adapter plugged in, these live readings show the part at work, when your car reports them:

Throttle position
Relative throttle position
Absolute throttle position B
Accelerator pedal position D
Accelerator pedal position E
Commanded throttle actuator

What to do

Have it checked this week. The car remains usable, but the fault will not clear itself and will fail the roadworthiness test.

Clearing a code switches the light off but repairs nothing: if the fault remains, the code comes back. Clearing a fault code yourself →

How to read this code

PPowertrain
0standardised code
1Fuel and air metering
23P0123