Oxygen Sensor: Description and Operation

Oxygen Sensor Location:

An oxygen 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.

Oxygen Sensor Voltage:

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. Voltage output from the Oxygen Sensor is about 0.9 volts DC when the fuel air mixture is richer than stoichiometric and about 0.1 volts DC when the mixture is leaner than stoichiometric with a sharp voltage transition from high to low at the stoichiometric point. The ECU's instant mixture adjustment in response to the voltage output of the oxygen sensor causes the output voltage from the Oxygen Sensor to fluctuate rapidly between 0.1 and 0.9 volts DC and will be observed as an average of about 0.6 volts DC when measured with a voltmeter.