Code Definition

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

System: Powertrain  |  Type: Generic (OBD-II Standard)  |  Make: Generic

About P0123

P0123 is a generic (obd-ii standard) powertrain diagnostic trouble code. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P0123 is stored, the module has detected a signal or supply voltage higher than the expected operating range; and a sensor-related fault — the reported value from the named sensor is out of spec.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

Because P0123 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

The throttle or pedal position sensor A is supplied with a 5V reference from the ECM and returns a signal voltage proportional to throttle plate or accelerator pedal position, typically rising from around 0.5V at rest to approximately 4.5V at full travel. P0123 sets when the ECM measures sensor A signal voltage above the maximum threshold for a calibrated period, commonly above about 4.8V, which is higher than the sensor produces even at wide open throttle. The realistic causes are the signal wire shorted to the 5V reference or to a battery supply, an open sensor ground circuit allowing the si...

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