The P0120 code indicates a problem with the throttle position sensor (TPS) circuit, meaning the engine control module is not receiving the expected voltage signal from the TPS during engine operation.
The TPS may be damaged, have worn contacts, or be misaligned, causing incorrect voltage readings.
Loose, corroded, or damaged wiring and connectors between the TPS and the engine control module can disrupt the signal.
A low or unstable voltage supply or poor ground connection to the TPS can trigger the code.
Physical obstruction or wear in the throttle body can affect sensor operation.
In rare cases, the PCM may misinterpret sensor data, but this is less common than sensor or wiring faults.
Replacing the TPS is often the most effective solution, but first verify the sensor’s output and inspect wiring and connectors to rule out other causes.
The PCM is rarely the source of this code; most cases stem from the sensor or its wiring. Replacing the PCM is usually unnecessary and costly.
A vacuum leak can cause idle issues, but it does not directly trigger P0120. Focus on the TPS circuit first.