ENGINE
<NON-TURBO>
-
Control
System
Catalyst Monitor
Current vehicles use a three-way catalytic converter
to reduce emission of harmful gases. The converters
are referred to as three-way because they specifical-
ly address three pollutants (hydrocarbons, carbon
Operation
02 sensors located above (upstream) and below
(downstream) the catalytic converter are able to
monitor the efficiency of the converter. The dual
02
sensor strategy is based on the fact that as
a catalyst deteriorates, it oxygen storage capacity
and efficiency are both reduced. By monitoring the
U71AK42AA
monoxide, and nitrogen oxide) produced in the com-
bustion chamber. The catalyst monitor uses a pair
:j
of inputs to indirectly measure just how effective
the catalyst is at reducing emissions.
oxygen storage capacity of the catalyst, its efficiency
can be indirectly calculated. The upstream sensor
detects the amount of oxygen in the exhaust gas
before it enters the converter. This sensor should
switch fairly rapidly.
Upstream
(primary)
--.,
Downstream
()ooo/
Engine
Exhaust
gas
AFUO089
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