P2122
Throttle/Pedal Position Sensor/Switch D Circuit Low Input
The appearance of the standard OBD2 trouble fault code P2122 is an indicator that your vehicle ECU triggered a threshold alert for "Throttle/Pedal Position Sensor/Switch D Circuit Low Input". Understanding the root component breakdown helps avoid expensive diagnostic fees.
Driver's Summary
Storing code P2122 is your car's way of telling you something is wrong with the throttle/pedal position sensor/switch d circuit low input. In practice, this fault causes lack of engine response when pressing the gas pedal. This is not a code to ignore — the underlying fault can rapidly worsen and lead to costly repairs if driving continues.
Symptoms
Lack of engine response when pressing the gas pedal
Common Causes
- Short to ground in pedal sensor wiring
- Failed Accelerator Pedal Position (APP) sensor
- Water in the floorboard corroding connector
- Failed PCM
How to Fix
- 1 Repair shorted wire
- 2 Replace accelerator pedal assembly
- 3 Dry out carpet and clean connector
- 4 Test PCM reference voltage
Technical Explanation
The ECM detects code P2122 by continuously monitoring the relevant sensor circuit against calibrated threshold values stored in its non-volatile memory. The control module samples the circuit continuously during normal operation, using both voltage level monitoring and frequency analysis to detect open circuits, shorts to ground, shorts to battery voltage, and high-resistance connections. The fault remains stored in memory even after the MIL is cleared; it becomes a confirmed DTC after failing two consecutive drive cycles, and the PCM logs a freeze frame record of the engine's exact operating state at the moment of detection.
Is It Safe to Drive?
With P2122 active, your engine or transmission is not operating within design parameters. Short-term driving may seem fine, but internal damage is accumulating — particularly to short to ground in pedal sensor wiring.
Mechanic's Pro Tip
The most common mistake with P2122 is replacing the sensor without verifying the reference voltage and ground integrity first. Use a scan tool to monitor the sensor's live output; a truly failed sensor shows a stuck, flatlined reading — a sensor that fluctuates but reads slightly off usually indicates a wiring or vacuum issue, not a dead sensor. Always spray electrical contact cleaner on the connector pins before condemning the sensor.
Pedal assembly: $150 - $350