Chevrolet 1993 S-10 Pickup Owner's Manual page 120

Features & Controls
Malfunction Indicator Lamp (Service Engine Soon)
Standard Cluster Digital Cluster
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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 comes
on
while you are driving,
the computer is indicating that you have a problem. You should take your
vehicle in for service soon.
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