BAS brake booster, component description - GF42.31-P-4004GZ
MODEL 164 up to Model Year 08
The BAS brake booster (A7/7) is installed in the left major assemblies compartment. Like a conventional brake booster it assists the foot force of the driver when braking and carries out the BAS brake application.
BAS brake servo
(section drawing)
An emergency brake application is determined by the ESP control unit through the diaphragm travel sensor (A7/7b1). With a BAS brake application the BAS solenoid valve (A7/7y1) opens the valve (d) which introduces atmospheric pressure from the vehicle interior via the air cleaner (g and f) to the backs of the rolling diaphragms (c).
The full assistance pressure from the brake servo is transmitted to the master brake cylinder via the output rod (h). If the brake application has ended, then the ESP control unit receives a signal from the BAS release switch (A7/7s1) and the BAS solenoid valve is closed again. The BAS assistance is terminated.