LAUNCH TECH CRT511, User Manual

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2.6.2 non-Continuous Monitors
“Non-continuous” Monitors perform and complete their testing once per trip.
The “non-continuous” Monitors are:
1. o
2
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.
The oxygen sensor must reach a temperature of at least 600-650°F, and the
engine must reach normal operating temperature, for the computer to enter
into closed-loop operation.
The oxygen sensor only functions when the computer is in closed-loop. A
properly operating oxygen sensor reacts quickly to any change in oxygen
content in the exhaust stream. A faulty oxygen sensor reacts slowly, or its
voltage signal is weak or missing.
The Oxygen Sensor Monitor is supported by “spark ignition” vehicles only.
The Oxygen Sensor 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.
2. o
2
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
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.
The Misfire Monitor is supported by both “spark ignition” vehicles and
“compression ignition” vehicles.
2. fuel System Monitor
This Monitor uses a Fuel System Correction program, called Fuel Trim, inside
the on-board computer. Fuel Trim is a set of positive and negative values that
represent adding or subtracting fuel from the engine. This program is used
to correct for a lean (too much air/not enough fuel) or rich (too much fuel/not
enough air) air-fuel mixture. The program is designed to add or subtract fuel,
as needed, up to a certain percent. If the correction needed is too large and
exceeds the time and percent allowed by the program, a fault is indicated by
the computer.
The Fuel System Monitor is supported by both “spark ignition” vehicles and
“compression ignition” vehicles. The Fuel System Monitor may be a “One-Trip”
or “Two-Trip” Monitor, depending on the severity of the problem.
3. Comprehensive Components Monitor (CCM)
This Monitor continuously checks all inputs and outputs from sensors,
actuators, switches and other devices that provide a signal to the computer.
The Monitor checks for shorts, opens, out of range value, functionality and
“rationality* ( See Note ).”
Rationality: Each input signal is compared against all other inputs and against
information in the computer’s memory to see if it makes sense under the current
operating conditions.
Example: The signal from the throttle position sensor indicates the vehicle is
in a wide-open throttle condition, but the vehicle is really at idle, and the idle
condition is confirmed by the signals from all other sensors. Based on the input
data, the computer determines that the signal from the throttle position sensor
is not rational (does not make sense when compared to the other inputs). In this
case, the signal would fail the rationality test.
The CCM is supported by both “spark ignition” vehicles and “compression
ignition” vehicles. The CCM may be either a “One-Trip” or a “Two-Trip”
Monitor, depending on the component.