Launch CReader 3001, User Manual

Page: 18 / 37

LAUNCH 3001
User’s Manual
13
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
OBD2 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.