On Board Diagnosis Logic
WARNING: This page is about a different car, the 2004 Nissan Sentra. However, it is still accessible from the selected car via links, so may be relevant.
To judge the malfunction, the diagnosis checks that the A/F signal computed by ECM from the air fuel ratio (A/ F) sensor 1 signal fluctuates according to fuel feedback control.
Courtesy of NISSAN MOTOR CO., U.S.A.