Innova 3100 Owner's Manual page 42

Learning More
OBD 2 MONITORS
Misfire Monitor - This Monitor continuously checks for engine
misfires. A misfire occurs when the air-fuel mixture in the cylinder
does not ignite. The misfire Monitor uses changes in crankshaft
speed to sense an engine misfire. When a cylinder misfires, it no
longer contributes to the speed of the engine, and engine speed
decreases each time the affected cylinder(s) misfire. The misfire
Monitor is designed to sense engine speed fluctuations and
determine from which cylinder(s) the misfire is coming, as well as
how bad the misfire is. There are three types of engine misfires,
Types 1, 2, and 3.
- Type 1 and Type 3 misfires are two-trip monitor faults. If a fault
is sensed on the first trip, the computer temporarily saves the
fault in its memory as a Pending Code. The MIL is not
commanded on at this time. If the fault is found again on the
second trip, under similar conditions of engine speed, load and
temperature, the computer commands the MIL "On," and the
code is saved in its long term memory.
- Type 2 misfires are the most severe type of misfire. When a Type
2 misfire is sensed on the first trip, the computer commands the
MIL to light when the misfire is sensed. If the computer
determines that a Type 2 misfire is severe , and may cause
catalytic converter damage, it commands the MIL to "flash" once
per second as soon as the misfire is sensed. When the misfire is
no longer present, the MIL reverts to steady "On" condition.
Catalyst Monitor - The catalytic converter is a device that is
installed downstream of the exhaust manifold. It helps to oxidize
(burn) the unburned fuel (hydrocarbons) and partially burned fuel
(carbon monoxide) left over from the combustion process. To
accomplish this, heat and catalyst materials inside the converter
react with the exhaust gases to burn the remaining fuel. Some
materials inside the catalytic converter also have the ability to
store oxygen, and release it as needed to oxidize hydrocarbons
and carbon monoxide. In the process, it reduces vehicle emissions
by converting the polluting gases into carbon dioxide and water.
The computer checks the efficiency of the catalytic converter by
monitoring the oxygen sensors used by the system. One sensor is
located before (upstream of) the converter; the other is located
after (downstream of) the converter. If the catalytic converter loses
its ability to store oxygen, the downstream sensor signal voltage
becomes almost the same as the upstream sensor signal. In this
case, the monitor fails the test.
The Catalyst 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.
40 OBD 2