Faulty accelerator pedal position sensor (APPS) assembly; Damaged or corroded wiring in the sensor 'D' circuit; Loose or poor electrical connection at the sensor or ECM; Failed ECM (less common); Water intrusion or contamination in the connector; Aftermarket or improperly installed electronic throttle control components

DTC codes / P21xx · Fuel and air metering / P2120

P2120Throttle/Pedal Position Sensor/Switch 'D' Circuit

Q: What does code P2120 mean?

Throttle/Pedal Position Sensor/Switch 'D' Circuit. P2120 indicates that the engine control module (ECM) has detected an abnormal signal from the throttle or pedal position sensor circuit designated as 'D'. This sensor is typically part of a redundant pair that reports the driver's accelerator pedal input, and the ECM sets this code when the voltage on the 'D' circuit falls outside the expected range or does not correlate with the other sensor signals.

P2120 indicates that the engine control module (ECM) has detected an abnormal signal from the throttle or pedal position sensor circuit designated as 'D'. This sensor is typically part of a redundant pair that reports the driver's accelerator pedal input, and the ECM sets this code when the voltage on the 'D' circuit falls outside the expected range or does not correlate with the other sensor signals.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
Reduced engine power or limp mode, limiting acceleration
Hesitation or stumble when pressing the accelerator pedal
Unresponsive or delayed throttle response
In some cases, the engine may idle erratically or stall

Common causes, most likely first

Faulty accelerator pedal position sensor (APPS) assembly
Damaged or corroded wiring in the sensor 'D' circuit
Loose or poor electrical connection at the sensor or ECM
Failed ECM (less common)
Water intrusion or contamination in the connector
Aftermarket or improperly installed electronic throttle control components

How to diagnose and fix it

Inspect the accelerator pedal sensor connector for corrosion, looseness, or water intrusion and clean or repair as needed
Check the wiring harness for chafing, breaks, or short circuits between the sensor and the ECM
Measure the sensor 'D' signal voltage with a scan tool or multimeter and compare to manufacturer specifications
Perform a throttle relearn or calibration procedure if the sensor has been replaced or disconnected
Replace the accelerator pedal position sensor assembly if voltage readings are out of range
Test the ECM connector and pins for tightness and signal integrity
If all else fails, replace and reprogram the ECM as a last resort

Common Misdiagnosis of P2120

Many technicians replace the accelerator pedal assembly without first checking the wiring harness for intermittent shorts, which is a frequent cause of this code.
A weak or failing battery or charging system can cause voltage drops that mimic sensor 'D' circuit faults, so always verify battery health before condemning the sensor.
The 'D' circuit is often one of two or three redundant sensors; a failure in one may not cause drivability issues but will still set the code, leading some to ignore it until limp mode occurs.
Aftermarket floor mats or debris can physically obstruct the pedal and cause the sensor to report implausible values, setting P2120 without any electrical fault.
On some vehicles, a faulty brake pedal switch or cruise control switch can interfere with the throttle position signal and trigger this code, so check related switches.

Can I keep driving with P2120?

You can usually drive the vehicle with P2120, but expect reduced engine power and possible limp mode. Avoid heavy acceleration and have the fault diagnosed promptly to prevent sudden loss of power.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.