P0121 — Throttle/Pedal Position Sensor "A" Range/Performance
The throttle position sensor (TPS) signal does not match the expected range for the commanded pedal position. On drive-by-wire vehicles, two redundant sensors are compared; a divergence between them or implausible motion triggers this code.
General code reference. Confirm the definition and diagnostic procedure for your vehicle's year, model and engine. A stored code alone does not identify a failed part.
Affected components
- Throttle position sensor
- Throttle body
- Accelerator pedal sensor
Possible causes to check
These are possible checks, not a ranked diagnosis. Follow the vehicle manufacturer's test procedure before replacing parts.
- TPS contact track worn (older potentiometer-type sensors)
- Carbon buildup blocking throttle plate
- Corroded TPS connector
Possible symptoms
- Check engine light on
- Reduced throttle response, possible limp mode
- Hesitation or surging
- Idle too high or too low
Diagnostic notes
- The malfunction indicator lamp may illuminate
- This code can affect emissions
- A drive cycle may be required after repair
- Reduced-power or limp mode may occur
Related codes
Sources
Check each reference's vehicle and model-year scope. General background links do not establish which fault is most likely on your vehicle.
Diagnostic information is provided for reference only. Confirm the code with a compatible scan tool and follow the vehicle manufacturer's service procedures before replacing components.