Legacy Outback Ltd Sedan F4-2.5L SOHC (2000)
Oxygen Sensor: Description and Operation
Front Oxygen (A/F) Sensor
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The front oxygen (A/F) sensor uses zirconium oxide (ZrO2) which is a solid electrolyte, at portions exposed to exhaust gas.
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The zirconium oxide has the property of generating electromotive force when contacting an oxygen ion, and the electromotive force generated
varies depending on the amount of oxygen ion.
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The front oxygen (A/F) sensor detects the amount of oxygen in exhaust gases in a linear form by making use of this property. The sensor housing
is grounded to the exhaust pipe, and the inside is connected to the ECM through the harness.
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A ceramic heater is employed to improve performance at low temperature.
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When rich air-fuel mixture is burnt in the cylinder, the oxygen in the exhaust gases reacts almost completely through the catalytic action of the
platinum coating on the surface of the zirconia tube. This results is a very large difference in the oxygen concentration between the inside and
outside, and the electromotive force generated is large.
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When a lean air-fuel mixture is burnt in the cylinder, oxygen remains in the exhaust gases even after the catalytic action, and this results in a small
difference in the oxygen concentration. The electromotive force is very small.
