Brake Booster: Inspection: Operation
WARNING: This page is about a different car, the 2013 Nissan Xterra. However, it is still accessible from the selected car via links, so may be relevant.
With engine stopped, change vacuum to atmospheric pressure by depressing brake pedal several times. Then with brake pedal fully depressed, start engine and when vacuum pressure reaches the standard, make sure that clearance between brake pedal and floor panel decreases.