Launch BST580D User Manual page 16

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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.
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 )."
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BST580D User's Manual