P0122: Throttle/Pedal Position Sensor/Switch "A" Circuit Low
The throttle or pedal position sensor A voltage is lower than the computer allows, as if the throttle were reading below fully closed.
What P0122 means
Throttle position sensors normally put out somewhere around 0.5 volts at idle and rise to about 4.5 volts at full throttle. P0122 sets when the sensor A signal drops below the lowest value the computer accepts. That usually means the signal wire is shorted to ground, the 5 volt reference feeding the sensor is missing, or the sensor has failed. KBB notes that you will usually be able to drive, but with reduced performance, and that professionals discourage driving that way for long. On drive-by-wire cars, the computer may lock the throttle near idle or limit power because it cannot trust your pedal input. Shops check the live voltage with the key on, then back probe the connector for 5 volts, ground and signal. If several sensors that share the 5 volt reference have low codes, they hunt for the short that is dragging the circuit down. Replacing the sensor without testing the wiring is a common mistake, according to RepairPal.
Common symptoms
- Check engine light on
- Hesitation or stalling
- Hard starting
- Car stuck in reduced power mode
- Often no other symptoms on older cars
Most common causes
- Faulty throttle position sensor
- Signal wire shorted to ground
- Open 5 volt reference wire
- Corroded or damaged connector
- Accelerator pedal sensor failure on drive-by-wire cars
What to check yourself first
Unplug and inspect the throttle body and pedal sensor connectors. Follow the harness for rubbed spots. Check whether other sensors on the same 5 volt reference, like the MAP sensor, also have low voltage codes, which points to a wiring short.
Typical fixes and what they cost
| Fix | Typical cost | Note |
|---|---|---|
| Replace throttle position sensor | $185-$258 | When the sensor itself fails with good wiring. |
| Replace throttle body | $623-$766 | If the sensor is integrated into the electronic throttle body. |
| Electrical diagnosis to find a wiring or connector fault | $122-$179 | RepairPal lists poor connections and chafed wiring as a common misdiagnosis. |
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
- P0123 Throttle/Pedal Position Sensor/Switch "A" Circuit High
- P0120 Throttle/Pedal Position Sensor/Switch "A" Circuit
- P0121 Throttle/Pedal Position Sensor/Switch "A" Circuit Range/Performance
- P2135 Throttle/Pedal Position Sensor/Switch "A"/"B" Voltage Correlation
- P0107 Manifold Absolute Pressure/Barometric Pressure Circuit Low