P0121: Throttle/Pedal Position Sensor/Switch "A" Circuit Range/Performance
The throttle or pedal position sensor A signal does not match what the computer expects from other sensors like airflow and RPM.
What P0121 means
P0121 means the throttle or pedal position sensor A is sending a signal, but it is irrational. RepairPal explains the code triggers when the circuit sends data that does not make sense to the computer. For example, the throttle reads 40 percent open while airflow and manifold pressure say the engine is at idle. A worn spot on the sensor track, carbon build up that keeps the throttle from closing properly, and connection problems are common causes. RepairPal even lists torn or jammed floor mats, which can hold the pedal slightly down. On drive-by-wire cars the computer also cross checks two sensors, and when they disagree it often cuts power to keep the car safe. Shops graph the sensor voltage while slowly opening and closing the throttle, looking for a smooth line without glitches. They compare it with MAF and MAP readings and inspect the throttle body. Replacing the sensor or throttle body usually fixes it once wiring is confirmed good.
Common symptoms
- Check engine light on
- Hesitation or stumbling on acceleration
- Hard starting
- Erratic idle
- Reduced power mode on some vehicles
Most common causes
- Worn throttle position sensor with a dead spot
- Dirty or carbon-filled throttle bore
- Floor mat jamming the accelerator pedal
- Corroded or loose connector
- Sensor A and sensor B readings disagreeing
What to check yourself first
Make sure nothing is pressing on the gas pedal, like a stacked floor mat. Inspect the throttle body for carbon and clean it with throttle body cleaner if your owner manual allows it. Check the sensor connectors for corrosion.
Typical fixes and what they cost
| Fix | Typical cost | Note |
|---|---|---|
| Replace throttle position sensor | $185-$258 | For separate sensors on cable throttle engines. |
| Replace throttle body | $623-$766 | On electronic throttle cars, where the sensor is built into the throttle body. |
| Electrical diagnosis to find a wiring or connector fault | $122-$179 | For connector or wiring resistance that skews the signal. |
Typical US price ranges for parts and labor, not quotes. Your shop should confirm the cause with a diagnostic before replacing parts.
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Related codes
- P0120 Throttle/Pedal Position Sensor/Switch "A" Circuit
- P0122 Throttle/Pedal Position Sensor/Switch "A" Circuit Low
- P0123 Throttle/Pedal Position Sensor/Switch "A" Circuit High
- P2135 Throttle/Pedal Position Sensor/Switch "A"/"B" Voltage Correlation
- P0101 Mass or Volume Air Flow "A" Circuit Range/Performance