Checking Brake Fluid Level

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

Check fluid level in reservoir tank. It should be between the "Max" and "Min" lines on reservoir tank.
If fluid level is extremely low, check brake system for leaks.
Release parking brake lever and see if brake warning lamp goes off. If not, check brake system for leaks.

Fig 1: Checking Brake Fluid Level

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