Throttle/Pedal Position Sensor/Switch "D" Circuit Low
Diagnostic trouble code P2122 indicates that the powertrain control module (PCM) has detected a voltage signal from the Throttle/Pedal Position Sensor/Switch 'D' that falls below the minimum expected threshold. This typically points to an electrical issue, such as a short to ground, within the accelerator pedal position sensor circuit.
This code is highly urgent because a failure in the drive-by-wire system can cause the vehicle to lose throttle response or enter a restricted 'limp mode' while driving. It should be diagnosed and repaired immediately to ensure safe vehicle operation.
Common symptoms
- Illuminated Check Engine Light
- Lack of response when pressing the accelerator pedal
- Vehicle enters reduced power or 'limp' mode
- Engine idles roughly or erratically
- Hesitation or stalling when attempting to accelerate
Likely causes
- Faulty Accelerator Pedal Position (APP) sensor
- Wiring short to ground in the sensor 'D' signal circuit
- Open circuit or broken wire in the sensor 'D' harness
- Corroded, damaged, or loose electrical connector at the APP sensor
- Faulty Powertrain Control Module (PCM) (rare)
What to check before replacing parts
Visually inspect the APP sensor wiring harness and connector.
Look for: Look for chafed wires, melted insulation, or corroded pins that could cause a short to ground or open circuit.
Monitor APP sensor 'D' voltage using a live data scan tool.
Look for: Observe the voltage while slowly pressing the pedal; it should smoothly increase without dropping out. A reading stuck near 0V indicates a hard fault.
Verify the 5-volt reference and ground circuits at the APP sensor connector.
Look for: Using a multimeter, ensure the sensor is receiving a steady 5 volts and has a solid ground. Missing voltage points to a wiring or PCM issue.
Perform a continuity and short-to-ground test on the signal wire between the sensor and the PCM.
Look for: Disconnect both ends and check for resistance to ground. Any continuity to ground on the signal wire confirms a short in the harness.
Test the APP sensor itself using a multimeter or oscilloscope.
Look for: Check the resistance or voltage sweep of the sensor's 'D' circuit while moving the pedal. Erratic readings, dead spots, or no change in resistance indicates an internally failed sensor.
This page explains the generic P2122 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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