Heated Oxygen Sensor (HO2S)
WARNING: This page does not describe the selected car, but rather 9 other vehicles, including the 2000 Nissan Xterra, 2000 Nissan Sentra, 2000 Nissan Quest, 2000 Nissan Pathfinder, and 2000 Nissan Maxima. However, it is still accessible from the selected car via links, so may be relevant.
HO2S sensor monitors amount of oxygen in exhaust gas. Sensor provides a voltage signal which is used to adjust air/fuel mixture to obtain optimum combustion. HO2S heater quickly brings sensor to operating temperature, reducing time engine is in open loop mode.
A rich exhaust gas mixture causes high sensor voltage (0.6-1.0 volt). A lean exhaust gas mixture causes low sensor voltage (0.1-0.3 volt). ECM monitors signal from sensor and adjusts air/fuel mixture accordingly.