P0123: OBD-II code P0123 means the throttle position sensor A is reporting a signal higher than possible — typically an open ground or a failed sensor.

Symptoms

• Check engine light is on, often with reduced-power mode active and a warning message on the dashboard.
• Poor throttle response, high idle, or the throttle may feel stuck open due to a falsely high reading.
• The vehicle may refuse to rev beyond a limp-mode limit or behave erratically under acceleration.

Common causes

• A failed TPS/APP sensor with an internally stuck-high signal element.
• An open ground wire between the sensor and the PCM, pulling the signal to reference voltage.
• A corroded connector or a signal wire shorted to 5 V reference or battery voltage.

What to do?

Read live TPS voltage — a stuck-at-5 V reading confirms open ground or a shorted sensor. Check ground continuity from the sensor connector to the PCM. Backprobe the signal wire and sweep the pedal — voltage should rise smoothly. Replace the sensor and perform a throttle relearn.