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OBD II Definitions
Powertrain Control Module (PCM)
– OBD II terminology for the on-board
computer that controls engine and drive train.
Malfunction Indicator Light (MIL)
– Malfunction Indicator Light (Service
Engine Soon, Check Engine) is a term used for the light on the instrument
panel. It is to alert the driver and/or the repair technician that there is a
problem with one or more of vehicle's systems and may cause emissions to
exceed federal standards. If the MIL illuminates with a steady light, it
indicates that a problem has been detected and the vehicle should be
serviced as soon as possible. Under certain conditions, the dashboard light
will blink or flash. This indicates a severe problem and flashing is intended
to discourage vehicle operation. The vehicle onboard diagnostic system
cannot turn the MIL off until necessary repairs are completed or the
condition no longer exists.
DTC
– Diagnostic Trouble Code (DTC) that identifies which section of the
emission control system has malfunctioned.
Enabling Criteria
– also termed Enabling Conditions. They are the
vehicle-specific 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.
OBD II Drive Cycle
– a specific mode of vehicle operation that provides
conditions required to set all the readiness monitors applicable to the
vehicle
to the “Ready” condition. The purpose of completing an OBD II drive
cycle is to force the vehicle to run its onboard diagnostics. Some form of a
drive cycle needs to be performed after DTCs have been erased from the
PCM’s memory or after the battery has been disconnected. Running
through a vehicle’s complete drive cycle will “set” the readiness monitors so
that future faults can be detected. Drive cycles vary depending on the
vehicle and the monitor that needs to be reset. For vehicle specific drive
cycle,
consult the vehicle’s Owner’s Manual.
Freeze Frame Data
– when an emission related fault occurs, the OBD II
system not only sets a code but also records a snapshot of the vehicle
operating parameters to help in identifying the problem. This set of values is
referred to as Freeze Frame Data and may include important engine
