1995 GMC Sonoma Owner's Manual - Page 106

Indicator Lights Indicator lights goon when you use your turn signals, change from low beam headlights to high beams, or when you use your hazard flashers. The next few pages will also tell you about the indicator lights on your vehicle and helpyou locate them. Malfunction Indicator Lamp (SERVICE ENGINE SOON Light) The amber Malfunction Indicator Lamp (SERVICE ENGINE SOON Light) is located at the top of your instrument panel. SERVICE ENGINE SOON A computer monitors operation of your fuel, ignition and emission control systems. Thislight 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 itcomes on while you are driving, the computeris 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 awhile the emission controls won't work well, your fuel economy as won't be as good and your engine may not run as smoothly. This could lead to costly repairs not covered by your warranty. If Your Vehicle is Equippedwith OBD I/ Certain vehicles with 4.3 liter engines are equipped with a new emission diagnostic system. You can tell whether your vehicle has this system by reading your tune-up label located under the hood. If the label says "OBD 11" on it, the following instructions apply. 2-60