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2.6 OBD II Definitions
Powertrain Control Module (PCM)
Malfunction Indicator Light (MIL)
DTC --
Enabling Criteria --
OBD II Drive Cycle -- A
Freeze Frame Data
-- OBD II terminology for the
on-board compute that controls engine and drive train.
-- Malfunction Indicator Light
(Service Engine Soon, Check Engine) is a term used for the light on
the instrument panel. It is t o 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 can not turn
the MIL off until the necessary repairs are completed or the condition
no longer exists.
Diagnostic Trouble Codes (DTC) that identify which section
of the emission control system has malfunctioned.
Also termed Enabling Conditions. They are the
vehicle-spcific 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.
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.
-- 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
flow, engine load, fuel pressure, fuel trim value, engine coolant
temperature, ignition timing advance, or closed loop status.
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