Draft guidance: awaiting Claude spot-check, qualified-mechanic review and named-editor approval. Do not use a fault code alone to replace parts.
P0123: Throttle/pedal position sensor or switch “A” circuit high
The control unit is seeing voltage above the permitted range from throttle or accelerator-position circuit “A”.
What P0123 means
The control unit is seeing voltage above the permitted range from throttle or accelerator-position circuit “A”. This is the electrical counterpart to P0122, although either fault can cause similar drivability and fail-safe behaviour.
Can I still drive?
Stop and arrange recovery if the engine revs unexpectedly, throttle response is erratic, the vehicle surges, stalls or enters limp mode. Do not test an unpredictable throttle in traffic. A direct, low-speed trip to a garage is only a reasonable boundary when the warning is steady and the pedal response, idle and acceleration remain entirely normal.
Symptoms
- Engine-management warning.
- Uneven or high idle.
- Hesitation, surging or stalling.
- Reduced power or limp mode.
- Poor acceleration.
- Increased fuel use.
- Apparently uncommanded acceleration on some fault strategies.
Common causes
- Open sensor-earth circuit.
- Signal wire shorted to the 5-volt reference or another powered wire.
- Loose, wet or corroded connector.
- Broken, trapped or chafed loom.
- Failed throttle-position sensor or integrated electronic throttle body.
- Incorrect sensor installation or adjustment on older designs.
- Control-unit failure only after the circuit and components have been excluded.
Safe first checks
- Record all codes and freeze-frame data; related throttle-correlation codes matter. Switch the ignition off and inspect connectors and visible wiring at the throttle body and pedal. Look for loom damage near the inlet manifold, engine cover and heat shielding, including wiring stretched or trapped during previous work. Do not repeatedly run an erratic engine, force the electronic throttle plate or replace the full assembly before its reference, earth and signal circuits have been tested.
Typical UK fix cost
Approximately £90–£450 for diagnosis and a typical wiring, connector, sensor or throttle-body repair. Integrated sensors often require a complete throttle-body assembly; unusually expensive parts or poor access may exceed this editorial range.
Related models
This is a generic OBD-II code used across many makes and models. The exact test thresholds, component layout and repair route vary by engine and manufacturer, so check vehicle-specific technical information before ordering parts.
Related fault codes
- P0121: Throttle/pedal position sensor or switch “A” range/performance
- P0122: Throttle/pedal position sensor or switch “A” circuit low
- P0128: Coolant temperature below thermostat regulating temperature
- P0130: Oxygen/lambda sensor circuit malfunction, Bank 1 Sensor 1
Sources
- Honda service information — P0122/P0123 thresholds and diagnostic paths (PDF)
- GM service information mirror — P0122/P0123 diagnostic table
- Toyota service information — P0120/P0123 circuit diagnostics
- Fixter — UK throttle-body replacement cost guide
A diagnostic trouble code identifies a system or circuit to investigate. It does not prove that a named part has failed. Preserve freeze-frame data and seek a vehicle-specific diagnosis before clearing the code.