Oxygen Sensor: Description and Operation

O2 Sensor:

PURPOSE
The Oxygen Sensor (O2S) is the primary input to the fuel delivery system. Used to measure the O2 content in the exhaust gas.

LOCATION
The oxygen sensor is located on the exhaust manifold to detect the concentration of oxygen in the exhaust gases.

CONSTRUCTION AND OPERATION
It consists of the zirconia element (with thin platinum surface coating) which generates electromotive force, lead wire which draws out the electromotive force and cover and housing which 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 faces. 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 outside 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.

A large concentration difference results in about 1V of the electromotive force and a small difference results in about 0V. In other words, if the amount of oxygen in the exhaust gases is less (air-fuel mixture is richer than the stoichiometric mixture), about 1V of electromotive force is generated, and if it is more (air-fuel mixture is leaner than the stoichiometric mixture), almost none is generated.

In this way, the oxygen sensor detects whether the oxygen concentration is high or low (or the mixture is leaner or richer than the stoichiometric mixture).