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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 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.
