GMC 1999 Savana Van Owner's Manual page 126

NOTICE:
Modifications made to the engine, transmission,
exhaust or fuel system of your vehicle or the
replacement of the original tires with other than
those of the same Tire Performance Criteria
(TPC) can affect your vehicle's emission controls
and may cause the SERVICE ENGINE SOON
light to come on. Modifications to these systems
could lead to costly repairs not covered by your
warranty. This may also result in a failure to pass
a required Emission Inspection/Maintenance test.
2-58
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:
D
--
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.
D
--
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.
If the Light Is Flashing
The following may prevent more serious damage to
your vehicle:
D
Reducing vehicle speed.
D
Avoiding hard accelerations.
D
Avoiding steep uphill grades.
D
If you are towing a trailer, reduce the amount of
cargo being hauled as soon as it is possible.
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