Brake Booster Vacuum Assist

Brake Booster Vacuum Assist Description and Operation

System Component Description

The Brake Booster Vacuum Assist system consists of the following:

Brake Booster Auxiliary Vacuum Pump
- The Brake Booster Vacuum Pump is a secondary vacuum supply to the brake booster used to maintain sufficient vacuum for brake assist.

Brake Booster Vacuum Sensor
- The vacuum sensor is used to measure the level of vacuum available in the brake booster. The Electronic Brake Control Module supplies a 5 V reference and a low reference circuit to the brake booster vacuum sensor. The vacuum sensor is located in the brake booster or vacuum hose. The Brake Booster Vacuum Sensor supplies a voltage signal in relation to the pressure in the brake booster to the Electronic Brake Control Module.

Electronic Brake Control Module
- The Electronic Brake Control Module monitors the vacuum in the brake booster using the Brake Booster Vacuum Sensor. When the vacuum within the system drops, below 42 kPa (6 psi) the Electronic Brake Control Module turns ON the Brake Booster Auxiliary Vacuum Pump by providing a ground to the Brake Booster Pump Relay. The relay activates and supplies voltage to the Brake Booster Auxiliary Vacuum Pump. The Electronic Brake Control Module shuts the pump off when the vacuum pressure is above 55 kPa (8 psi) by removing the ground to the Brake Booster Pump Relay.

Vacuum Brake Booster
- When brake system input force is applied, air at atmospheric pressure is admitted to the rear of both vacuum diaphragms, providing a decrease in brake pedal effort required. When input force is removed, vacuum replaces the atmospheric pressure within the booster. The booster uses source vacuum to decrease the effort required by driver when applying the brake.

Vacuum Source
- Vacuum is supplied by the engine vacuum or by the Brake Booster Auxiliary Vacuum Pump.

System Operation

The pump can be switched on and off by the Electronic Brake Control Module based on the required vacuum. Pressure variations during braking can be measured, and the pump can be activated to generate additional vacuum if required to increase the braking force.

The pump runs for the first 5 seconds after engine running to perform a self test. Engine running, the pump may run another 30 seconds and then turns off, due to the timer relay. The pump has a maximum run time of 180 seconds per ignition cycle with engine running, when it reaches the maximum run time the pump shuts down to cool off and will not allow the pump to run again until the next engine run cycle.