LAUNCH TECH CRT511 User Manual page 11

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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 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.
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 efficiency 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
signal voltage becomes almost the same as the upstream sensor signal. In
this case, the monitor fails the test.
The Catalyst Monitor is supported by "spark ignition" vehicles only. The
Catalyst 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.
4. Heated Catalyst Monitor
Operation of the "heated" catalytic converter is similar to the catalytic
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converter. The main difference is that a heater is added to bring the catalytic
converter to its operating temperature more quickly. This helps reduce
emissions by reducing the converter's down time when the engine is cold. The
Heated Catalyst Monitor performs the same diagnostic tests as the catalyst
Monitor, and also tests the catalytic converter's heater for proper operation.
The Heated Catalyst Monitor is supported by "spark ignition" vehicles only.
This Monitor is also a "Two-Trip" Monitor.
5. egr (exhaust gas recirculation) System Monitor
The Exhaust Gas Recirculation (EGR) system helps reduce the formation
of Oxides of Nitrogen during combustion. Temperatures above 2500°F
cause nitrogen and oxygen to combine and form Oxides of Nitrogen in
the combustion chamber. To reduce the formation of Oxides of Nitrogen,
combustion temperatures must be kept below 2500°F. The EGR system
recirculates small amounts of exhaust gas back into the intake manifold,
where it is mixed with the incoming air/fuel mixture. This reduces combustion
temperatures by up to 500°F. The computer determines when, for how long,
and how much exhaust gas is recirculated back to the intake manifold. The
EGR Monitor performs EGR system function tests at preset times during
vehicle operation.
The EGR Monitor is supported by both "spark ignition" vehicles and
"compression ignition" vehicles. The EGR 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.
6. eVaP System Monitor
OBD II vehicles are equipped with a fuel Evaporative system (EVAP) that
helps prevent fuel vapors from evaporating into the air. The EVAP system
carries fumes from the fuel tank to the engine where they are burned during
combustion. The EVAP system may consist of a charcoal canister, fuel tank
cap, purge solenoid, vent solenoid, flow monitor, leak detector and connecting
tubes, lines and hoses.
Fumes are carried from the fuel tank to the charcoal canister by hoses or
tubes. The fumes are stored in the charcoal canister. The computer controls
the flow of fuel vapors from the charcoal canister to the engine via a purge
solenoid. The computer energizes or deenergizes the purge solenoid
(depending on solenoid design). The purge solenoid opens a valve to allow
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