BAS brake booster, component description - GF42.31-P-4004RC
MODEL 171.4 as of model year 09 /YoM 08 model refinement package
A7/7 BAS brake booster; A7/7b1 BAS diaphragm travel sensor; A7/7s1 BAS release switch; B34/1 ESP brake pressure sensor 1
Location The brake booster is located on the left of the engine compartment.
Task The brake booster boosts the pedal force applied by the driver during braking. In the event of an emergency stop, the Brake Assist (BAS) function is also activated.
Design The BAS brake booster contains the following electrical components: BAS diaphragm travel sensor - BAS release switch - ESP brake pressure sensor 1 - BAS solenoid valve (A7/7y1)
Function The brake booster is constantly supplied with vacuum via a vacuum line. If the brake is not actuated, equal vacuum exists on both sides of the diaphragm. A push spring holds the diaphragm plate in its starting position. During the brake application outside air is lead to the back of the diaphragm via a port. Between the front and rear chamber of the brake booster, a pressure difference occurs which acts in the direction of the master brake cylinder and thus boosts the pedal force applied by the driver.