Circuit/System Description
WARNING: This page is about a different car, the 2008 Chevrolet Malibu. However, it is still accessible from the selected car via links, so may be relevant.
The engine control module (ECM) uses the inputs from the brake fluid pressure sensor to monitor and control the hill start assist function. The EBCM receives a serial data message to command the HCU valves closed to maintain the applied brake pressure when the vehicle is stopped. The ECM will command the EBCM to open the valves and release the pressure after the engine restarts.