Diagnostic trouble code P2120 indicates a malfunction in the 'D' circuit of the throttle/pedal position sensor. This sensor tells the engine control module how far the accelerator pedal is pressed, and a fault can lead to reduced engine power or a limp-in mode.
The sensor itself may have failed internally, causing an incorrect or missing signal on circuit D. This is the most common cause.
Worn, broken, or corroded wires or connectors in the sensor circuit can disrupt the signal, triggering the code.
Loose terminals, bent pins, or moisture in connectors can cause intermittent or permanent circuit faults.
In some vehicles, the throttle position sensor itself may be the source of the circuit D fault, especially if it shares a reference voltage or ground.
Although rare, a damaged PCM can cause circuit D faults. This should only be considered after thoroughly testing all other components and wiring.
You may be able to drive, but the vehicle will likely enter a reduced-power or limp mode to prevent damage. Acceleration will be limited, and driving at highway speeds may be difficult. It is best to have the issue diagnosed and repaired promptly.
Replacing the sensor is a common and often effective repair, but it is important to first verify that the wiring and connectors are in good condition. A faulty sensor is the most likely cause, but a wiring issue could also be the culprit.
No. The PCM is rarely the cause of P2120. Many drivers are incorrectly told to replace the computer, but this is almost never necessary. Focus on the sensor, wiring, and connections first.
Circuit D refers to a specific signal circuit within the throttle/pedal position sensor assembly. Many vehicles have multiple sensors (A, B, C, D) for redundancy. P2120 indicates a fault in the D circuit, which could be the sensor itself or the wiring for that circuit.