Service Repair Manual

GENERAL (FBC)
5. Oxygen Sensor
1) The oxygen sensor installed on the exhaust manifold
makes use of the principles of solid electrolyte oxygen
concentration cell. The‘ oxygen concentration cell is
characterized by sharp change of the output voltage in
the vicinity of the stoichiometric air-fuel ratio.
2) Using such characteristics, the oxygen sensor senses the
oxygen concentration in the exhaust gas and feeds it to
the ECU. The ECU then judges if the air-fuel ratio is
richer or leaner as compared to the stoichiometric ratio
and provides feedback control to adjust the air-fuel ratio
to the stoichiometric ratio where the emission purifi-
cation rate of the three way catalytic converter is the
optimum.
6. Vacuum Switch
The vacuum switch is a contact type switch that is operated
by intake manifold vacuum. When the throttle valve closes,
the intake manifold vacuum acts on the vacuum switch to
close its contact.
By this action, the voltage on the ECU side is grounded and
the ECU senses that the throttle valve opening is near idle.
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