Buick 1998 Century Owner's Manual page 136

This system is called OBD I1 (On-Board
Diagnostics-Second Generation) and is intended to assure
that emissions are at acceptable levels for the life of the
vehicle, helping to produce a cleaner environment. The
SERVICE ENGINE SOON light comes on and a chime
will sound to indicate that there is a problem and service is
required. Malfunctions often will be indicated by the
system before any problem is apparent. This may prevent
more serious damage to your vehicle. This system is also
designed to assist your service technician in correctly
diagnosing any malfunction.
NOTICE:
If you keep driving your vehicle with this light
on, after a while, your emission controls may not
work as well, your fuel economy may not be as
good and your engine may not run as smoothly.
This could lead to costly repairs that may not be
covered by your warranty.
This light should come on, as a check to show you it is
working, when the ignition is on and the engine is not
running. If the light doesn't come on, have it repaired.
This light will also come on during a malfunction in one
of two ways:
Light Flashing
--
A misfire condition has been
detected. A misfire increases vehicle emissions and
may damage the emission control system on your
vehicle. Dealer or qualified service center diagnosis
and service may be required.
Light On Steady -- An emission control system
malfunction has been detected on your vehicle.
Dealer or qualified service center diagnosis and
service may be required.
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