Launch Creader Professional 909E User Manual page 19

LAUNCH
Professional 909E User Manual
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 engine vacuum to draw the
fuel vapors from the canister into the engine where the vapors are burned. The
EVAP Monitor checks for proper fuel vapor flow to the engine, and pressurizes
the system to test for leaks. The computer runs this Monitor once per trip.
The EVAP Monitor is supported by "spark ignition" vehicles only. The EVAP
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 PCM commands the MIL "On," and saves the code in its long-
term memory.
7. Secondary Air System Monitor
When a cold engine is first started, it runs in open-loop mode. During open-
loop operation, the engine usually runs rich. A vehicle running rich wastes
fuel and creates increased emissions, such as carbon monoxide and some
hydrocarbons. A Secondary Air System injects air into the exhaust stream to aid
catalytic converter operation:
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