Users Manual Part 2

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MDMAXLITEA
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:
• It supplies the catalytic converter with the oxygen it needs
to oxidize the carbon monoxide and hydrocarbons left over
from the combustion process during engine warmup.
• The extra oxygen injected into the exhaust stream also
helps the catalytic converter reach operating temperature
more quickly during warm-up periods. The catalytic
converter must heat to operating temperature to work
properly.