Mazda CX-9 Brake Booster giving you problems. Is the pedal soft and the pads are good.Some CX-9's may exhibit a condition that the brake pedal is harder than usual to depress. An air leakage (hissing) sound may be heard from the driver-side foot area during braking. Might need a new Genuine Mazda CX-9 replacement vacuum brake booster. Comes with new style brake light switch also.