Sensors And Switches - Subaru LEGACY 2002 Quick Reference Index

Fuel Injection (Fuel System)
When rich air-fuel mixture is burnt in the cylinder, the oxygen in the exhaust gases is almost
!
completely used in the catalytic reaction by the platinum coating on the external surface of the zir-
conia tube. This results in a very large difference in the oxygen ion concentration between the in-
side and outside of the tube, and the electromotive force generated is large.
When a lean air-fuel mixture is burnt in the cylinder, relatively large amount of oxygen remains
!
in the exhaust gases even after the catalytic action, and this results in a small difference in the
oxygen ion concentration between the tube's internal and external surfaces. The electromotive
force in this case is very small.
! The difference in oxygen concentration changes drastically in the vicinity of the stoichiometric
air-fuel ratio, and hence the change in the electromotive force is also large. By using this informa-
tion, the ECM can determine the air-fuel ratio of the supplied mixture easily. The front oxygen sen-
sor does not generate much electromotive force when the temperature is low. The output
characteristics of the sensor stabilize at a temperature of approximately 700°C (1,292°F).
Atmospheric air

SENSORS AND SWITCHES

FU-20
Lean Air-fuel ratio Rich
B2H2006B