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9
DN606 Automotive Diagnostic Tool User's Manual
In order for the OBD monitor system to become ready, the vehicle should be
driven under a variety of normal operating conditions. These operating conditions
may include a mix of highway driving and stop and go, city type driving, and at
least one overnight-off period. For specic information on getting your vehicle’s
OBD monitor system ready, please consult your vehicle owner’s manual.
2.5 OBD II Terminology
The following terms and their denitions are related to OBD II systems. Read
and reference this list as needed to aid in the understanding of OBD II systems.
Powertrain Control Module (PCM) -- The PCM is the OBD II accepted term
for the vehicle’s “on-board computer.” In addition to controlling the engine
management and emissions systems, the PCM also participates in controlling
the powertrain (transmission) operation. Most PCMs also have the ability to
communicate with other computers on the vehicle (ABS, ride control, body, etc.).
Monitors -- Monitors are “diagnostic routines” programmed into the PCM. The
PCM utilizes these programs to run diagnostic tests, and to monitor operation
of the vehicle’s emissions-related components or systems to ensure they
are operating correctly and within the vehicle’s manufacturer specifications.
Currently, up to fteen Monitors are used in OBD II systems. Additional Monitors
will be added as the OBD II system is further developed.
Note: Not all vehicles support all een Monitors.
Enabling Criteria -- Also termed Enabling Conditions. They are the vehicle-
specic events or conditions that must occur within the engine before the various
monitors will set, or run. Some monitors require the vehicle to follow a prescribed
“drive cycle” routine as part of the enabling criteria. Drive cycles vary among
vehicles and for each monitor in any particular vehicle. Please refer to the
vehicle’s factory service manual for specic enabling procedures.
Trip - A Trip for a particular Monitor requires that the vehicle is being driven in
such a way that all the required “Enabling Criteria” for the Monitor to run and
complete its diagnostic testing are met. The “Trip Drive Cycle” for a particular
Monitor begins when the ignition key is turned “On.” It is successfully completed
when all the “Enabling Criteria” for the Monitor to run and complete its diagnostic
testing are met by the time the ignition key is turned “Off.” Since each of the
fifteen monitors is designed to run diagnostics and testing on a different part
of the engine or emissions system, the “Trip Drive Cycle” needed for each
individual Monitor to run and complete varies.
OBD II Drive Cycle -- A specific mode of vehicle operation that provides
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