Description And Operation: Description

Heated Oxygen Sensor (HO2S), consisting of zirconium and alumina, is installed on both upstream and downstream of the Manifold Catalytic Converter (MCC) to detect the air/fuel ratio and send it to the Engine Control Module (ECM).
In order that this sensor operates properly, the temperature of the sensor tip must be higher than 370°C (698°F). For this reason, a heater controlled by the ECM duty signal, is built into the sensor.
When the exhaust gas temperature is lower than the specified value, the heater warms the sensor tip.

Courtesy of KIA MOTORS AMERICA, INC.