P0120
Throttle Position Sensor / Switch A Circuit Malfunction
The ECU detects a general electrical fault on the throttle position sensor/switch A circuit. Signal missing, implausible, or wiring broken. Generic catch-all when no more specific TPS-A code applies.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Symptoms
- Check engine light on
- Reduced throttle response, possible limp mode
- Hesitation or surging
- Idle too high or too low
Common causes
Ordered by how often each turns out to be the cause.
- TPS worn or failed (dead spot in resistive track)Common
- TPS wiring or connector faultPossible
- TPS mechanically misaligned to throttle shaftLess likely
Parts involved
- Throttle Position Sensor
- TPS Wiring
- TPS Connector
- Throttle Body
P0120 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.