OBD
II Malfunction Indicator Lamp (MIL)
When
the ignition switch is initially turned on and the engine is not
running, the malfunction indicator lamp lights for a bulb check. While
the engine is running, the MIL will light only if there is an
emissions-related concern.
The
on board diagnostic (OBD) generation two (II) system continuously
monitors all engine and transmission sensors and actuators looking for
electrical faults, as well as values that do not logically (rationally)
fit with other powertrain data. When certain operating conditions are
met and a comprehensive monitor detects a failure that will result in
emissions exceeding a predetermined level, the computer stores a
diagnostic trouble code, and illuminates the MIL.
The
OBD II system also actively tests some systems for proper operation
while the vehicle is being driven. Fuel control and engine misfire are
checked continuously, catalyst efficiency, exhaust gas recirculation
operation, evaporative system integrity, oxygen sensor response, and
the oxygen sensor heaters are tested once per trip when prerequisite
operating conditions are met. The computer will illuminate the MIL if
during these prerequisite operating conditions the system detects a
failure that will result in emissions exceeding a predetermined level.
Whenever
an engine misfire severe enough to damage the catalytic converter is
detected, the MIL will blink on and off.
Once
lit, the MIL will remain on until the vehicle has completed three
consecutive good trips (three trips in which the fault is not
detected). The MIL is also turned OFF when stored diagnostic trouble
codes are cleared. However, the MIL will only remain OFF if the fault
is successfully repaired. For more information
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