Innova 3100 Owner's Manual page 44

Learning More
OBD 2 MONITORS
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 OBD 2 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.
Oxygen Sensor Heater Monitor - The Oxygen Sensor Heater
Monitor tests the operation of the oxygen sensor's heater. There
are two modes of operation on a computer-controlled vehicle:
"open-loop" and "closed-loop." The vehicle operates in open-loop
when the engine is cold, before it reaches normal operating
temperature. The vehicle also goes to open-loop mode at other
times, such as heavy load and full throttle conditions. When the
vehicle is running in open-loop, the oxygen sensor signal is
ignored by the computer for air/fuel mixture corrections. Engine
efficiency during open-loop operation is very low, and results in the
production of more vehicle emissions.
Closed-loop operation is the best condition for both vehicle
emissions and vehicle operation. When the vehicle is operating in
closed-loop, the computer uses the oxygen sensor signal for
air/fuel mixture corrections.
In order for the computer to enter closed-loop operation, the
oxygen sensor must reach a temperature of at least 600°F. The
oxygen sensor heater helps the oxygen sensor reach and maintain
its minimum operating temperature (600° F) more quickly, to bring
the vehicle into closed-loop operation as soon as possible.
The Oxygen Sensor Heater 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.
Oxygen Sensor Monitor - The Oxygen Sensor monitors how much
oxygen is in the vehicle's exhaust. It generates a varying voltage of
up to one volt, based on how much oxygen is in the exhaust gas,
and sends the signal to the computer. The computer uses this signal
to make corrections to the air/fuel mixture. If the exhaust gas has a
large amount of oxygen (a lean air/fuel mixture), the oxygen sensor
generates a "low" voltage signal. If the exhaust gas has very little
oxygen (a rich mixture condition), the oxygen sensor generates a
"high" voltage signal. A 450mV signal indicates the most efficient,
and least polluting, air/fuel ratio of 14.7 parts of air to one part of fuel.
42 OBD 2