What P0121 Means
The throttle position sensor is sending a signal that's outside the range the engine control module expects for normal operation.
Common Causes
- Faulty throttle position sensor
- Dirty or worn throttle body
- Damaged wiring or connector to the sensor
Symptoms You Might Notice
- Hesitation or jerky acceleration
- Idle may surge or fluctuate
- Check engine light on
- In some cases the car may enter a reduced-power 'limp' mode
What to Check First
- 1
Clean the throttle body, since dirt buildup is a common cause of erratic sensor readings
- 2
Inspect the sensor's wiring and connector for damage
- 3
Test the sensor's voltage output through its full range of motion; replace if it doesn't track smoothly