Subaru 2002 Impreza Service Manual page 66

SENSORS AND SWITCHES
Fuel Injection (Fuel System)
4. Sensors and Switches
A: FRONT OXYGEN (NF) SENSOR
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The front oxygen sensor uses zirconium oxide (Zr02) which is a solid electrolyte, at portions ex-
posed to exhaust gas.
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The zirconium oxide has the property of generating electromotive force when its both sides are
exposed to oxygen ions of different concentration and the magnitude of this electromotive force
depends on how much the difference is.
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The front oxygen sensor detects the amount of oxygen in exhaust gases by making use of this
property of the zirconium oxide material.
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The zirconium oxide material is formed into a closed end tube and its external surface is ex-
posed to exhaust gases with smaller oxygen ion concentration, whereas its internal surface is ex-
posed to atmospheric air. The external surface has a porous platinum coating. The sensor housing
is grounded to the exhaust pipe and the inside is connected to the ECM through the harness to
be able to use the current output from the sensor.
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The sensor incorporates a ceramic heater to improve its performance at low temperatures.
(1 ) Protection tube
(2) Gasket
NF0389
(3)
Sensor housing
(4) Ceramic heater
FU-16