Operational Check
WARNING: This page is about a different car, the 2004 Nissan Altima, 2003 Nissan Altima, and 2002 Nissan Altima. However, it is still accessible from the selected car via links, so may be relevant.
With engine off, depress brake pedal several times until pedal height no longer changes. Press and hold brake pedal down. Start engine. If pedal goes down slightly, power brake unit is okay. If pedal does not move, check for air leak.