Equus 3110 - CanOBD2 Diagnostic Tool - Manual (Page 29)

CAN OBD2 27
E
Onboard Diagnostics
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 refrig-
erant 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 cor-
rections.
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 oper-
ating 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 sig-
nal 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 oxy-
gen (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.