Equus 3150 - ABS/SRS + OBD2 Diagnostic Tool - Manual (Page 27)

Onboard Diagnostics
OBD2 MONITORS
OBD2 25
Exhaust Gas Recirculation (EGR) 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 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.
Evaporative System (EVAP) 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 de-energizes 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 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.
Air Conditioning (A/C) Monitor - The A/C Monitor senses leaks
in air conditioning systems that utilize R-12 refrigerant. Vehicle
manufacturers have been given two options:
1.
Use R-12 refrigerant in their A/C systems, and integrate an A/C
Monitor in the OBD2 systems of these vehicles to detect for
refrigerant leaks; or
2.
Use R-134 refrigerant instead of R12. The A/C Monitor is not
required on these vehicles.
To date, all vehicle manufacturers have opted to use R-134 in their A/C
systems. As a result, this Monitor has not yet been implemented.