User guide

AutoEnginuity ScanTool User Guide 55
tive. This is called Adaptation or Fuel Trim. LTFT values represent
the average of Short Term Fuel Trim fuel corrections.
MAF or Mass Air Flow Sensor
Normally mounted as part of the air cleaner assembly, it measures
air flow into the intake manifold. The MAF sensor generates a con-
tinuous signal that varies nearly linearly with true mass air flow.
MAP or Manifold Absolute Pressure Sensor
Senses the difference between the atmospheric pressure and the
pressure (or vacuum) inside the intake manifold. It is also used to
calculate the engine load.
MIL or Malfunction Indicator Light
Check Engine or Service Engine Soon indicator light is used to
alert the vehicle operator that a fault has occurred. The MIL is only
used to indicate problems in the emissions control system. It is not
inteded to be used as a maintenance reminder, e.g., change oil.
When the vehicle’s engine computer senses that a part or
component is operating outside of the normal range or not reporting
at all, a fault is recorded in the stored DTC area of memory.
When a severe misfire occurs that could damage the catalytic
converter, the MIL is will flash on and off once per second. A
flashing MIL is intended to discourage vehicle operation until
repairs have been performed.
Misfire
A miss in the ignition firing process of cylinder combustion due to
the failure of the fuel/air mixture to ignite.
Misfire Monitor
A continuously run monitor that checks for a miss in the ignition
firing process of cylinder combustion. If the misfire is small, a
Pending DTC will be recorded. If the misfire is large enough to
cause damage or allow emissions to exceed 1.5 times the EPA stan-
dard, a stored DTC is recorded immediately and the MIL is illumi-
nated. If the misfire is severe and capable of causing damage to the
catalytic converter, the MIL will flash once per second as long as