ENGINE <NON-TURBO>
-
Control System
I-41
A functioning converter stores oxygen so it can be
L
used for oxidation of hydrocarbons (HC) and carbon
monoxide (CO). The downstream sensor detects
a lower oxygen level in the exhaust than the
up-
stream sensor. It indicates this by switching at a
significantly slower rate than the upstream sensor.
As the converter deteriorates and loses its ability
to store oxygen, the switch rate at the downstream
oxygen sensor approaches that of the upstream
sensor. The system is monitored so that when the
switch rate of the downstream sensor reaches 90%
of the switch rate of the upstream sensor (automatic
transmissions), the MIL is illuminated. The threshold
for manual transmissions is 70%. At this point,
ex-
haust emissions are projected to exceed 1 l/z times
the legal limit.
Upstream
02
Stoich
A/F
/
Downstream
02
lzFgjE+
Low oxygen
storage
Downstream
02
low
catalyst
b-
-
eff
icikncy
I
\dw@
I
-
-
AFU0090
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