Users Manual Part 2

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MDMAXLITEA
completed their diagnosis and testing, and which ones have
not yet run and completed testing and diagnosis of their
designated sections of the vehicle’s emissions system.
The I/M Readiness Monitor Status function also can be used
(after repair of a fault has been performed) to confirm that
the repair has been performed correctly, and/or to check for
Monitor Run Status.
Tap on [I/M Readiness] from the Automotive main menu
screen, the screen will start reading the I/M readiness and
display the result.
Fig. 5-37
Currently, fifteen Monitors are supported by OBD II systems.
Additional monitors may be added as a result of Government
regulations as the OBD II system grows and matures. Not
all vehicles support all fifteen Monitors. Additionally, some
Monitors are supported by “spark ignition” vehicles only,
while others are supported by “compression ignition”
vehicles only.
Monitor operation is either “Continuous” or “Non-
Continuous,” depending on the specific monitor.
5.5.1 Continuous Monitors
Some of the vehicle components or systems are continuously
tested by the vehicle’s OBD 2 system, while others are
tested only under specific vehicle operating conditions. The
continuously monitored components listed below are always
ready:
1. 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.