Oxygen Sensor: Description and Operation

Fig. 159 Oxygen Sensor Voltage:

An oxygen (Lambda) sensor is used to provide more precise control of air/fuel mixtures. This system operates by measuring oxygen content in exhaust gases, as the amount of oxygen remaining in the exhaust gases is directly proportional to the air/fuel ratio of mixtures entering the engine.
The oxygen sensor is made of a ceramic material called zirconium dioxide. The inner and outer surfaces of the ceramic material are coated with a very thin layer of platinum. The outer surface is exposed to the exhaust gasses, while the inner surface is exposed to the outside air.

Fig. 124 Oxygen Sensor (PGM_CARB):

The difference in the amount of oxygen contacting the inner and outer surfaces of the oxygen sensor creates a pressure differential which results in a voltage signal being generated. The amount of voltage produced is determined by the air/fuel mixture. A high voltage (0.7 to 1.0 Volts) indicates a rich mixture, and a low voltage (0.0 to 0.3 Volts) indicates a lean mixture.