Hill Start Assist (Hill Hold Brake Delay Valves) 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.

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 stopped on a hill, the engine may shut off. When the driver releases the brake pedal, the engine will restart, but the vehicle may have a increased tendency to roll during the restart sequence.

The hill start assist feature minimizes vehicle rolling during the transition between brake release and engine restart. The brake delay valves maintain pressure in the brake lines, even though the pedal is released, until the engine starts. Brake cylinder pressure is then released following engine restart by opening the brake delay valves.

The brake delay valves are actuated through a vehicle wiring harness by a PWM signal provided by the generator control module. The brake delay valve assembly is a serviceable component.