Owner's Manual for the vehicle. With a quick reference ... - E38.org

158nOBD connector
An Illuminated indicator informs
you of the need for service, not
of the need to stop the vehicle.
However, the systems should be
checked by your BMW center at the
earliest possible opportunity.
When the filler cap is not properly
tightened, the OBD system can
detect the vapor leak and the indicator
will light up. If the filler cap is subsequently
tightened, the indicator should
extinguish within a few days.<
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The interface socket for the onboard diagnosis
system is located beneath a
cover on the center console front panel
(arrow).
A sticker with the text "OBD" is attached
to the cover.
The purpose of the OBD (Onboard
Diagnostic) system is to assure proper
emission control system operation for
the vehicle’s lifetime by monitoring
emission-related components and
systems for deterioration and malfunction.
Under certain conditions, the indicator
will blink or flash. This indicates a rather
severe level of engine misfire. When
this occurs, you should reduce speed
and consult the nearest BMW center as
soon as possible. Severe engine misfire
over only a short period of time can seriously
damage emission control components,
especially the catalytic converter.