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GLOSSARY
OBD2 Terminology
GLOSSARY
OBD2 TERMINOLOGY
The following terms and their denitions are related to OBD2 systems.
n Powertrain Control Module (PCM) - The PCM is the OBD2 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.).
n Monitor - 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 specications.
Currently, up to fteen Monitors are used in OBD2 systems. Additional Monitors will be added as the
OBD2 system is further developed.
NOTE: Not all vehicles support all fteen Monitors
n Enabling Criteria - Each Monitor is designed to test and monitor the operation of a specic part of the
vehicle’s emissions system (EGR system, oxygen sensor, catalytic converter, etc.). A specic set of
“conditions” or “driving procedures” must be met before the computer can command a Monitor to run
tests on its related system. These “conditions” are known as “Enabling Criteria.” The requirements and
procedures vary for each Monitor. Some Monitors only require the ignition key to be turned “On” for them
to run and complete their diagnostic testing. Others may require a set of complex procedures, such
as, starting the vehicle when cold, bringing it to operating temperature, and driving the vehicle under
specic conditions before the Monitor can run and complete its diagnostic testing.
n Complete / Incomplete - The terms “Complete” or “Incomplete” are used throughout this manual.
“Complete,” means the PCM has commanded a particular Monitor to perform the required diagnostic
testing on a system to ensure the system is operating correctly (within factory specications). The term
“Incomplete” means the PCM has not yet commanded a particular Monitor to perform diagnostic testing
on its associated part of the emissions system.
n 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 fteen 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.
n OBD2 Drive Cycle - An OBD2 Drive Cycle is an extended set of driving procedures that takes into
consideration the various types of driving conditions encountered in real life. These conditions may
include starting the vehicle when it is cold, driving the vehicle at a steady speed (cruising), accelerating,
etc. An OBD2 Drive Cycle begins when the ignition key is turned “On” (when cold) and ends when the
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