Circuit/System Description
WARNING: This page is about a different car, the 2009 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
The starter generator control module (SGCM) provides a ground to the hill hold relay. The relay provides voltage circuits to the hill hold solenoid valves (HHV). The SGCM controls the HHV through a pulse width modulated circuit closing the valves and maintaining brake pressure to the brakes when stopped to prevent vehicle roll forward or backward. The SGCM will open the valves releasing the brake pressure when the engine is started.