On Board Diagnosis Logic
WARNING: This page is about a different car, the 2004 Nissan Quest. However, it is still accessible from the selected car via links, so may be relevant.
To judge the malfunction, the A/F signal computed by ECM from the air fuel ratio (A/F) sensor 1 signal is monitored not to be shifted LEAN side or RICH side.
Courtesy of NISSAN MOTOR CO., U.S.A.