P0121Powertrain
Powertrain · SAE
Throttle/Pedal Position Sensor A Range/Performance
Meaning
The throttle position signal does not match the value the ECU expects from the other operating conditions. The sensor responds, but in an implausible or imprecise way.
Common causes
- Faulty throttle body or TPS potentiometer
- Carbon-fouled throttle plate that does not move smoothly
- Wiring or connector with excessive resistance or intermittent contact
- Vacuum leak that distorts the measured load
- Throttle adaptation not performed after a repair
Symptoms
- Hesitation and surging on acceleration
- Rough or fluctuating idle
- Possible limp mode (reduced power)
- Inconsistent throttle response
- Check-engine light on
Severity
Moderate: driving can become erratic and the car may enter limp mode, but there is no immediate mechanical risk.
What to do
- Read live throttle opening and compare it with the accelerator pedal position
- Clean the throttle body and confirm the plate moves freely
- Inspect the TPS wiring and connector for intermittent contacts
- Carry out the throttle adaptation/relearn specified by the manufacturer