Oxygen Sensor: Description and Operation

Exhaust Oxygen Sensor:

Oxygen Sensor:

Heated Oxygen Sensor Output:

The Oxygen sensor is located in the exhaust manifold. It detects the concentration of oxygen in the exhaust gases. It consists of the zirconia element, with a thin platinum surface coating, which generates an electromotive force. A lead wire draws out the electromotive force, and the cover and housing protect the zirconia element from damage. The zirconia element, by its property, generates the electromotive force when a difference in oxygen concentration exists between its surfaces. As its temperature rises, the change of the electromotive force is amplified by catalytic reaction of the platinum. The oxygen sensor makes use of this property. As atmosphere is introduced into the oxygen sensor, the inside of the zirconia element is exposed to the atmosphere and to exhaust gases. Thus the difference in concentration between the inside and the outside of the zirconia element varies with the oxygen concentration in the exhaust gases. The oxygen content in the exhaust reacts with the sensor to produce a voltage output. This voltage ranges from approximately 0.1 volt (high oxygen - lean mixture) to 0.9 volts (low oxygen - rich mixture). This voltage can be measured with a digital voltmeter having at least 10 M ohms input impedance. By monitoring the voltage output of the oxygen sensor, the ECM will know what fuel mixture command to give to the injector (lean mixture-low oxygen voltage = rich command, rich mixture-high oxygen voltage = lean command).