Positive Crankcase Ventilation
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2003 Nissan Xterra, 2003 Nissan Sentra, 2003 Nissan Pathfinder, 2003 Nissan Murano, and 2003 Nissan Maxima. However, it is still accessible from the selected car via links, so may be relevant.
With engine idling, remove vent hose from PCV valve. A hissing noise should be heard. Strong vacuum should be felt immediately when a finger is placed over valve inlet. Clean or replace PCV valve or hoses, if it does not operate as specified.