P0123 is set when the Powertrain Control Module (PCM) detects an abnormally high voltage on the throttle‑pedal position sensor/switch circuit. This typically means the sensor is reporting a “full‑open” condition even though the pedal is not pressed, or a short to a higher voltage source is present. The fault triggers the check‑engine light and can place the engine into a limp‑home mode with reduced power.
The sensor inside the pedal assembly can fail internally, causing it to output an excessively high voltage signal to the PCM.
A short‑to‑power, open ground, or broken wire in the sensor circuit can pull the signal high or create an open condition that the PCM interprets as high voltage.
Moisture, oxidation, or loose terminals at the pedal connector can increase resistance and produce an erroneously high voltage reading.
If the 5 V reference voltage or the ground path to the sensor is interrupted, the PCM may see the open circuit as a high‑voltage condition.
Non‑OEM pedals may have different electrical characteristics that do not match the PCM’s expectations, leading to a high‑voltage reading.
In rare cases the control module itself misinterprets the sensor data; this is the least common cause and should be verified before replacement.
The vehicle will likely run in a limited‑power limp‑home mode. You can drive short distances, but the reduced response means it’s wise to diagnose and repair the issue promptly.
Rarely. Most instances are caused by the sensor, wiring, or connectors. PCM failure is uncommon, so those components should be inspected before condemning the control module.
Yes, if the pedal houses an integrated position sensor, mechanical wear or electrical failure of that sensor can generate the same high‑voltage signal.
Related throttle‑position codes such as P0120‑P0122 or P0220‑P0222 often appear, helping to pinpoint whether the issue is in the sensor, circuit, or reference voltage.