Engine Control Module
WARNING: This page is about a different car, the 2005 Pontiac Pursuit and 2005 Chevrolet Cobalt. However, it is still accessible from the selected car via links, so may be relevant.
The ECM is the control center for the TAC system. The ECM determines the drivers intent and then calculates the appropriate throttle response. The ECM achieves throttle positioning by providing a pulse width modulated voltage to the TAC motor.