LAUNCH
3001
User’s Manual
11
generates a varying voltage of up to one volt, based on how much oxygen is in the
exhaust gas, and sends the signal to the computer. The computer uses this 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 efficient, 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 first 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. O2 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 efficiency 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)
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