Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
DTC P0121: Throttle Position Sensor Performance: Description
The Throttle Position (TP) sensor circuit provides a voltage signal that changes relative to throttle blade angle. PCM provides TP sensor with a 5-volt reference circuit and a low reference circuit. Rotation of TP sensor rotor from closed throttle position to Wide Open Throttle (WOT) position provides PCM with a signal voltage from less than one volt to greater than 4 volts through the TP sensor signal circuit. When conditions for running this DTC are met, PCM will use the MAP sensor to determine if the predicted operating range of TP sensor is correct.
A skewed MAP sensor may cause this DTC to set and should be tested for proper operation if TP sensor is determined to be operating properly and this DTC continues to set.
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.
When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.