Download The throttle actuator control (TAC) module contains a direct current actuator motor controlled by the ECM used to move the throttle plate (in either direction) and two throttle position sensors to determine throttle plate position. The throttle plate is held at a 7% rest position to a mechanical stop by a constant force return spring. This spring will hold the throttle plate to the stop when there is no current flowing to the actuator motor. There is another return spring, which creates constant force on the throttle plate only when the throttle plate is moved towards the full closed position. The ECM will monitor both the actuator motor and TP sensors for circuit faults, as well as check to make sure both springs can return the throttle to the 7% position no matter where the throttle plate remains.