Innova 3100 Owner's Manual page 43

Learning More
OBD 2 MONITORS
Heated Catalyst Monitor - Operation of the "heated" catalytic
converter is similar to the catalytic converter. The main difference
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
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 - OBD 2 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 com-
mands the MIL "On," and saves the code in its long-term memory.
OBD 2 41