BMW SERIE 3 CONVERTIBLE 2005 Owner's Manual page 149

OBD interface socket
engine misfiring for even a short period
of time can seriously damage emission
control system components, especially
the catalytic converter.
SERVICE ENGINE SOON warn-
ing lamp for Canadian models.
If the gas cap is not on tight
enough, the OBD system can
detect leaking vapor and the indicator
will light up. If the gas cap is then tight-
ened, the indicator will usually go out
after a short period of time.<
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