Oxygen Sensor: Description and Operation

Description

Heated Oxygen Sensors (HO2S) consists of zirconium and alumina and are installed both upstream and downstream of the Manifold Catalytic Converter (MCC).
The sensor looks at the difference between the oxygen in the atmosphere with the oxygen in the exhaust gas. The greater the difference in oxygen, the higher the voltage produced by the sensor. When A/F ratio is rich it generates approximately +1V and when the A/F ration is lean it is near 0V.
The sensor must be hot in order to operate normally. To keep it hot, the sensor has a heater which is controlled by the ECM via a duty cycle signal. When the exhaust gas temperature is lower than the specified value, the heater warms the sensor tip.