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
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 flow, 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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