Level 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.

Check that the brake fluid level in the reservoir tank is within specification, between the MAX and MIN lines as shown.
Visually check around reservoir tank for fluid leaks.
If fluid level is excessively low, check brake system for leaks.
If brake warning lamp remains illuminated after the parking brake pedal is released, check the brake system for any brake fluid leaks.

Fig 1: Checking Brake Fluid Level In Reservoir Tank

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