Hill Start Assist

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.

When a conventional vehicle is stopped on a hill, the brakes will hold the vehicle in place until the brake pedal is released. When a hybrid vehicle is completely stopped on a hill, the engine may shut off. When the driver releases the brake pedal, and applies the accelerator, the engine will restart. During the restart sequence, the vehicle may roll. Inputs and outputs from the following electronic control modules are required in order to accomplish a safe smooth transition during vehicle stops and starts:

Engine control module (ECM)
Electronic brake control module (EBCM)
Instrument panel cluster
Transmission control module
Starter generator control module

The hill start assist feature minimizes vehicle rolling during the transition between brake release and engine restart. The brake pressure modulator valve maintains pressure in the brake lines, even though the pedal is released, until the engine starts. Brake pressure is then release following engine restart.

The starter generator control module hill assist valves are actuated through the ECM controls. The ECM also commands the brake light signal required to the body control module (BCM) during the transition between engine off and engine start. The brake hill start assist valves are serviceable components.