Equus 3110 - CanOBD2 Diagnostic Tool - Manual (Page 28)

26 CAN OBD2
E
Onboard Diagnostics
OBD 2 MONITORS
Heated Catalyst Monitor - Operation of the “heated” catalytic
converter is similar to the catalytic converter. The main differ-
ence 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. This Monitor is also a “Two-Trip” Monitor.
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 recircu-
lated back to the intake manifold. The EGR Monitor performs EGR sys-
tem 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 com-
mands the MIL “On,” and saves the code in its long-term memory.
Evaporative System (EVAP) Monitor - OBD 2 vehicles are
equipped with a fuel Evaporative system (EVAP) that helps pre-
vent fuel vapors from evaporating into the air. The EVAP system car-
ries fumes from the fuel tank to the engine where they are burned dur-
ing combustion. The EVAP system may consist of a charcoal canister,
fuel tank cap, purge solenoid, vent solenoid, flow monitor, leak detec-
tor 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 pressur-
izes 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 com-
mands the MIL “On,” and saves the code in its long-term memory.