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.
|
