Oxygen Sensor: Description and Operation

Fig. 10 Oxygen (Lambda) Sensor:

The oxygen sensor, Fig. 10, is constructed of Zirconium dioxide, and the inner and outer surfaces are coated with platinum. The outer platinum surface is exposed to the exhaust gas while the inner surface is exposed to the outside air.
The oxygen sensor sends a variable voltage (0 - 1.0 vdc) to the electronic control unit depending on the difference between the amount of oxygen contacting the inner and outer surfaces of the sensor. The electronic control unit can then control the amount of fuel supplied to the engine in relation to oxygen content.