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 ash. This indicates a
severe problem and flashing is intended to discourage vehicle operation. The
vehicle onboard diagnostic system cannot turn the MIL off until the necessary
repairs are completed or the condition no longer exists.
DTC -- Diagnostic Trouble Codes (DTC) that identifies which section of the
emission control system has malfunctioned.
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.
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 specic drive cycle, consult the service manual.
Freeze Frame Data -- When an emissions 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 parameters such as
engine RPM, vehicle speed, air ow, engine load, fuel pressure, fuel trim value,
engine coolant temperature, ignition timing advance, or closed loop status.
Fuel Trim (FT) - Feedback adjustments to the base fuel schedule. Short-term
fuel trim refers to dynamic or instantaneous adjustments. Long-term fuel trim
refers to much more gradual adjustments to the fuel calibration schedule than
short-term trim adjustments. These long-term adjustments compensate for
vehicle differences and gradual changes that occur over time.
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