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11
LAUNCH
Professional 909E User Manual
signal to make corrections to the air/fuel mixture. If the exhaust gas has a large
amount of oxygen (a lean air/fuel mixture), the oxygen sensor generates a “low”
voltage signal. If the exhaust gas has very little oxygen (a rich mixture condition),
the oxygen sensor generates a “high” voltage signal. A 450mV signal indicates
the most efcient, and least polluting, air/fuel ratio of 14.7 parts of air to one part
of fuel.
The oxygen sensor must reach a temperature of at least 600-650°F, and the
engine must reach normal operating temperature, for the computer to enter into
closed-loop operation.
The oxygen sensor only functions when the computer is in closed-loop. A
properly operating oxygen sensor reacts quickly to any change in oxygen content
in the exhaust stream. A faulty oxygen sensor reacts slowly, or its voltage signal
is weak or missing.
The Oxygen Sensor Monitor is supported by “spark ignition” vehicles only. The
Oxygen Sensor Monitor is a “Two-Trip” monitor. If a fault is found on the rst trip,
the computer temporarily saves the fault in its memory as a Pending Code. The
computer does not command the MIL on at this time. If the fault is sensed again
on the second trip, the computer commands the MIL “On,” and saves the code in
its long-term memory.
2. O
2
Sensor Heater Monitor
The Oxygen Sensor Heater Monitor tests the operation of the oxygen sensor’s
heater. There are two modes of operation on a computer-controlled vehicle:
“open-loop” and “closed-loop.” The vehicle operates in open-loop when the
engine is cold, before it reaches normal operating temperature. The vehicle
also goes to open-loop mode at other times, such as heavy load and full throttle
conditions. When the vehicle is running in open-loop, the oxygen sensor signal is
ignored by the computer for air/fuel mixture corrections. Engine efciency during
open-loop operation is very low, and results in the production of more vehicle
emissions.
Closed-loop operation is the best condition for both vehicle emissions and
vehicle operation. When the vehicle is operating in closed-loop, the computer
uses the oxygen sensor signal for air/fuel mixture corrections.
In order for the computer to enter closed-loop operation, the oxygen sensor
must reach a temperature of at least 600°F. The oxygen sensor heater helps the
oxygen sensor reach and maintain its minimum operating temperature (600°F)
more quickly, to bring the vehicle into closed-loop operation as soon as possible.
The Oxygen Sensor Heater Monitor is supported by “spark ignition” vehicles
only. The Oxygen Sensor Heater Monitor is a “Two-Trip” Monitor. If a fault is
found on the rst trip, the computer temporarily saves the fault in its memory as
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