Impreza 2.5 RS Coupe F4-2.5L SOHC (2000)
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.
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The difference in oxygen concentration changes greatly in the vicinity of the optimum air-fuel ratio, and hence the change in the electromotive
force is also large. By inputting this information into the ECM, the air-fuel ratio of the supplied mixture can be determined easily. The oxygen
sensor does not generate much electromotive force when the temperature is low. The characteristics of the electromotive force stabilize at
temperature of approximately 300 to 400°C (572 to 752°F).