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P0121 Throttle Position Sensor Range/Performance Problem
What it means
The throttle position sensor (TPS) tells the computer how far the throttle is open. Its reading doesn't make sense compared with other sensors like airflow or engine speed, or it jumps around, so the computer suspects the sensor or its circuit.
Severity: Moderate
Can I drive it? Drive with caution. You may get hesitation, surging, a high or erratic idle, or the car may go into limp mode with reduced power. Get it checked soon.
Common causes (most likely first)
- Worn or faulty throttle position sensor
- Dirty or sticking throttle body
- Loose, corroded, or damaged TPS connector or wiring
- Failing electronic throttle body (on drive-by-wire cars, the TPS is often built in)
- Vacuum leak skewing the airflow comparison
Likely fixes
- Inspect the TPS connector and wiring
- Clean the throttle body
- Check the TPS signal for a smooth sweep with a scan tool or multimeter
- Replace the TPS or the whole electronic throttle body, then do a throttle relearn if required
DIY parts cost
$25–$300
Approximate estimate
Shop repair cost
$150–$700
Approximate estimate, parts + labor
DIY difficulty
Easy to Moderate
Varies by vehicle
Cost ranges are rough, approximate U.S. estimates and vary widely by vehicle, region, and parts brand. Always confirm the diagnosis before buying parts.
Parts you may need
- Throttle position sensorCheck price
- Throttle body cleanerCheck price
- Electronic throttle bodyCheck price
- Throttle body gasketCheck price
Affiliate links are placeholders. Verify fitment for your year/make/model.