Describes the details of testing the APP sensor. In many ways the APP or accelerator position sensor is a dual TPS connected to the gas pedal. Get the details on testing the APP. There are variations on testing the APP as opposed to a simple TPS. The APP is a central component of all drive-by-wire systems. The APP signals the ECM and ATC computer and it in turns actuates the throttle actuator. Get the scoop here. Learn to test these systems.