Chevrolet 1994 Blazer Owner's Manual page 125

Malfunction Indicator Light
(SERVICE ENGINE SOON)
Standard Cluster
A computer monitors operation of your fuel, ignition and emission control
systems. This light should come on when the ignition is on, but the engine is
not running, as a check to show you it is working. If it does not come on at
all, have it fixed right away. If it stays on, or it comes on while you are
driving, the computer is indicating that you have a problem. You should
take your vehicle in for service soon.
NOTICE:
If you keep driving your vehicle with this light on, after a while
the emission controls won't work as well, your fuel economy
won't be as good and your engine may not run as smoothly. This
could lead to costly repairs not covered by your warranty.
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