Heated Oxygen Sensor

Heated Oxygen Sensors (HO2S) 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, HO2S will begin functioning earlier than an unheated HO2S. Typically, there are at least two, one in front of and the other behind the catalytic converter (TWC). The HO2S in front of the TWC gives PCM feedback which is used to adjust fuel mixture. The HO2S behind the TWC is used to monitor TWC effectiveness by comparing readings between the two HO2Ss. If both HO2Ss are showing similar readings, TWC failure is indicated.