Heated Oxygen Sensor (HO2S)

HO2S sensors are located in exhaust system. When at operating temperature, sensor produces a voltage signal proportional to exhaust gas oxygen content. By heating up HO2S using a heating element, sensor will begin functioning earlier than an unheated sensor. Typically, there are at least two, one in front of and the other behind the catalytic converter (TWC). The sensor in front of the TWC gives PCM feedback which is used to adjust fuel mixture. The sensor behind the TWC is used to monitor TWC effectiveness by comparing readings between the two sensors. If both sensors are showing similar readings, TWC failure is indicated.