Optimized Hydraulic Braking System

If your vehicle is equipped with Electronic Stability Control and the optional 2.0L turbocharged engine (LNF), it also has a optimized hydraulic brake boost feature which supplements the power brake system to maintain consistent brake performance under conditions of low brake booster vacuum. Low brake booster vacuum conditions can include initial start up after the vehicle has been parked for several hours, very frequent brake stops, or high altitude driving. When hydraulic brake boost is active, you might feel a minor brake pulsation or movement in the pedal but this is normal.

The Optimized Hydraulic Brake Boost system activates (only) during a brake apply when the brake module detects low vacuum from the vacuum sensor mounted in the booster. The boost function in this case will be provided by the Electronic Stability Control system to provide metered brake pressure to the wheels. When the system activates to build pressure, the electronic control unit will run the pump motor, opens the electronic shuttle valve, and closes the isolation valves at the same time. The electronic control unit runs the pump in pulsed cycles and builds pressure in the wheels that exceeds the tandem main cylinder (with low vacuum in the booster). As the brake fluid is drained from the tandem main cylinder, the brakes pedal will move accordingly (pulsing feel in pedal). Pump speed and duration are controlled by computed volume models in the electronic control unit (information includes low vacuum sensed, tandem main cylinder pressure, and pedal travel through the brake apply sensor). If the pressure is reduced or vacuum restored while a low hydraulic boost is required the wheel pressure can then be continuously adjusted to the tandem main cylinder pressure by selectively lowering the current on the isolation valve.