System Description
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.
Courtesy of NISSAN MOTOR CO., U.S.A.
The ECM performs ON/OFF duty control of the heated oxygen sensor 1 heater corresponding to the engine speed and engine coolant temperature. The duty percent varies with engine coolant temperature when engine is started.