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10
LAUNCH Professional 919E User Manual
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 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) 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 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.
3. Catalyst Monitor
The catalytic converter is a device that is installed downstream of the exhaust
manifold. It helps to oxidize (burn) the unburned fuel (hydrocarbons) and
partially burned fuel (carbon monoxide) left over from the combustion process.
To accomplish this, heat and catalyst materials inside the converter react
with the exhaust gases to burn the remaining fuel. Some materials inside
the catalytic converter also have the ability to store oxygen, and release it
as needed to oxidize hydrocarbons and carbon monoxide. In the process,
it reduces vehicle emissions by converting the polluting gases into carbon
dioxide and water.
The computer checks the eciency of the catalytic converter by monitoring the
oxygen sensors used by the system. One sensor is located before (upstream
of) the converter; the other is located after (downstream of) the converter. If
the catalytic converter loses its ability to store oxygen, the downstream sensor
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