On-Board Diagnostics - BMW 1999-2005 M3 Service Manual

On-Board Diagnostics

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On-Board Diagnostics
(OBD II)
OBD II is an acronym for On-Board
Diagnostics II, the second generation of
on-board self-diagnostic equipment
requirements. These standards were
originally mandated for California
vehicles. Since 1996 they have been
applied to all passenger vehicles sold
in the United States.
On-board diagnostic capabilities are
incorporated into the hardware and
software of the engine control module
(ECM) to monitor virtually every
component that can affect vehicle
emissions. OBD II works to ensure that
the vehicles remain as clean as
possible over their entire life.
Each emission-influencing component
is checked by a diagnostic routine to
verify that it is functioning properly. If a
problem or malfunction is detected, the
OBD II system illuminates a warning
light on the instrument panel to alert
the driver. This malfunction indicator
light (MIL) will display the phrase
"Check Engine" or "Service Engine
Soon."
The OBD II system also stores
important information about the
detected malfunction so that a repair
technician can accurately find and fix
the problem.
Note:
Specialized OBD II scan tool
equipment is needed to access the
fault memory and OBD II data.
The OBD II fault memory
(including the MIL) can only be
OBD-2
2/25/2009 11:22 PM