ENGINE <NON-TURBO>
-
Control Svstem
Operation
Once it reaches its operating temperature of
572”
to
662”F,
the sensor generates a voltage inversely
proportional to the amount of oxygen in the exhaust.
This information is used by the PCM to calculate
the fuel injector pulse width necessary to provide
the critical 14.7 to 1 air/fuel ratio (stoichiometric).
A properly operating sensor must not only be able
to generate an output voltage across its operating
range of 0 to 1 volt as it is exposed to different
02
levels, it also must be able to detect these
changes quickly. To detect a shift in the air/fuel
mixture (lean or rich) the output voltage must change
beyond a threshold value. A malfunctioning sensor
could have difficulty changing beyond the threshold
value.
While there are existing tests that determine if an
02
sensor is shorted to voltage, contains an open
circuit, or does not function at all, prior to OBD
II, it was impossible to identify sluggish or marginal
sensors.
A slow response rate or reduced voltage output
are all signs of an improperly operating oxygen sen-
sor. This could mean longer instances of combustion
of less than optimum air/fuel mixtures. This can
significantly increase emissions.
The
02
sensor must have a voltage output of greater
than
.67
volt in order to pass the test. It must also
switch more times over a 120 second period than
a given threshold (to demonstrate quick response)
or produce a given number of steep slope switches
(demonstrating dynamic range and quick response)
over the same time period. Data is not stored unless
idle time exceeds 10 seconds.
Front
02
High switching
frequency
fast response
Front
O2
’
I
Low switching
frequency
slow response
E
.Q
2
.-
WE
Trigger 1.5 x STD
Switching frequency
AFUOO88
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