Summary
P0122 means the throttle position sensor (TPS) voltage has dropped below the minimum expected threshold — typically below 0.2V. The most common causes are a wiring short to ground (35%), a failed TPS (30%), and connector damage (20%). The engine will likely enter limp mode with severely limited power. Check the TPS connector and wiring first — a loose or damaged ground wire is a quick, cheap fix before replacing the sensor.
Severity: Moderate to High — limp mode limits drivability
Safe to drive: No — reduced power mode and potential stalling
Repair cost: $5–$400 depending on cause
DIY difficulty: Easy to Moderate
What does P0122 mean?
The throttle position sensor sends a voltage signal to the PCM indicating throttle plate angle. At closed throttle, the TPS typically reads around 0.5V. At wide-open throttle, it reads around 4.5V. The PCM uses this signal for fuel delivery calculations, ignition timing, and transmission shift strategy.
P0122 sets when the TPS voltage falls below the PCM's minimum threshold — usually under 0.2V — for a sustained period. This tells the PCM the signal is either shorted to ground, the sensor has failed low, or the signal wire has lost continuity. The PCM interprets this as "I can't trust the throttle input."
Most vehicles respond by entering a reduced power or limp mode, capping engine RPM to protect against uncontrolled acceleration. You'll feel a significant loss of power and the throttle may feel unresponsive.