1994 Cadillac DeVille Owner's Manual - Page 149

Malfinction Indicator Lamp (Service Engine Soon) A computer monitors operation of your fuel, ignition emission and 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 does it If not comeon atall, have it fixed right away. it stays on, or it comes on while you are driving, the computeris indicating that you have a problem You should take your vehicle infor 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 smoothly. This as could lead to costly repairs not coveredyour warranty. by 136