Airtight Check

WARNING: This page is about a different car, the 2006 Nissan Xterra. However, it is still accessible from the selected car via links, so may be relevant.

Run engine at idle for approximately 1 minute, and stop it after applying vacuum to booster. Depress brake pedal normally to change the vacuum to the atmospheric pressure. Make sure distance between brake pedal and floor panel gradually increases.
Depress brake pedal while engine is running and stop engine with pedal depressed. The pedal stroke should not change after holding pedal down for 30 seconds.

CAUTION: Depressing pedal interval is approximately 5 seconds.

Fig 1: Checking Brake Booster Airtightness

Courtesy of NISSAN MOTOR CO., U.S.A.