Oxygen Sensor: Description and Operation

Circuit Diagram:

HEATED OXYGEN SENSOR (HO2S)
The heated oxygen sensor senses the oxygen concentration in exhaust gas and converts it into a voltage which is sent to the PCM. For Zirconium type sensors, the oxygen sensor outputs about 1 V when the air fuel ratio is richer than the theoretical ratio, and outputs about 0 V when the ratio is leaner (higher oxygen concentration in exhaust gas.). The PCM controls the fuel injection ratio based on this signal so that the air fuel ratio is maintained at the stoichiometric ratio. The oxygen sensor has a heating element which ensures sensor performance during all driving conditions.