P2123 Subaru Throttle Pedal Position Sensor/Switch D Circuit Input High

Possible causes

– Faulty Accelerator Pedal Position (APP) Sensor
– Accelerator Pedal Position (APP) Sensor harness is open or shorted
– Accelerator Pedal Position (APP) Sensor circuit poor electrical connection
– Faulty Engine Control Module (ECM)

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)

P2123 Subaru Description

The Accelerator Pedal Position (APP) sensor is mounted on the accelerator pedal to detect the angle of the accelerator pedal. This sensor is electronically controlled and uses Hall-effect elements.

In the accelerator pedal position sensor, the voltage applied to terminals VPA and VPA2 of the Engine Control Module (ECM) changes between 0 V and 5 V in proportion to the angle of the accelerator pedal. The VPA is a signal to indicate the actual accelerator pedal angle and is used for the engine control. VPA2 is used to detect malfunctions of the sensor itself.

The ECM monitors the accelerator pedal angle from VPA and VPA2 signal outputs, and controls the throttle motor based on these signals.