Subaru LEGACY 2002 Quick Reference Index page 74

Fuel Injection (Fuel System)
4. Sensors and Switches
A: OXYGEN SENSOR (WITH CATALYTIC CONVERTER )
! The oxygen sensor is used to sense oxygen concentration in the exhaust gas. If the air-fuel ratio
is leaner than the stoichiometric ratio in the mixture (i.e., excessive amount of air), the exhaust gas
contains more oxygen. To the contrary, if the fuel ratio is richer than the stoichiometric ratio, the
exhaust gas contains almost no oxygen.
! Detecting the oxygen concentration in exhaust gas using the oxygen sensor makes it possible
to determine whether the air-fuel ratio is leaner or richer than the stoichiometry.
! The oxygen sensor has a zirconia tube (ceramic) which generates voltage if there is a difference
in oxygen ion concentration between the inside and outside of the tube. Platinum is coated on the
inside and outside of the zirconia tube as a catalysis and electrode material. The sensor housing
is grounded to the exhaust pipe and the inside is connected to the ECM through the harness.
! A ceramic heater is employed to improve performance at low temperatures.
(4)
(1) Zirconia tube
(2) Ceramic heater
(3) Protection tube
(4) Harness
(5) Sensor housing
(6) Gasket
SENSORS AND SWITCHES
(5)
FU-16
(3)
(2)
(1)
(6)
H2H1224D