P0123 — Throttle/Pedal Position Sensor/Switch A Circuit High

The controller detects an excessively high electrical input for throttle/pedal position sensor or switch channel A. The letter identifies a manufacturer-defined circuit, not necessarily a separate part. The limit concerns the electrical input, not directly how far the pedal is pressed.

Affected system: Powertrain

Symptoms

• Delayed, limited or absent accelerator response.
• Engine warning light and possible limp mode; idle may become uneven.

Possible causes

• Signal shorted to supply or an open sensor ground.
• Failed sensor or contaminated connector; causes depend on the channel’s circuit.

What to check

• Use the wiring diagram to identify channel A: throttle, pedal or switch; read accompanying faults on the other channels.
• Inspect channel A’s connector, terminals and harness; test reference supply and ground using the OEM pin assignment.
• Measure signal A and ground voltage drop; check shorts to supply or an open return using the wiring diagram.
• Check installation and mechanical travel after identifying the component; perform adaptation only when the repair procedure requires it.
• After repair, clear codes and recheck channel A under the original recorded conditions, following the manufacturer’s procedure.

Also written as: P0123-00, P012300, PO123 (some scan tools add the fault-type byte, e.g. -00).