1996 GMC Sonoma Owner's Manual - Page 105

Engine Coolant Temperature Gage This gage shows the engine coolant temperature. I f the gage pointer moves into the red area, your engine is too hot! TEMP Malfunction Indicator Lamp (Service Engine Soon Light) Your vehicle is equipped with a computer which monitors operation of the fuel, ignition and emission control systems. SERVICE ENGINE SOON It means that your engine coolanthas overheated. If you have been operating your vehicle under normal driving conditions, you should pull off the road, stop your vehicle and turn off the engine as soon as possible. This system is called OBD I1 (On-Board Diagnostics-Second Generation) and is intended toassure that emissions are at acceptable levels for the life of the vehicle, helping to producea cleaner environment. (In Canada, OBD I1 is replaced by Enhanced Diagnostics.) The SERVICE ENGINE SOON light comes on to indicate that there is a problem and service is required. Malfunctions often will be indicated by the system before any problem is apparent, which may prevent more serious damage to your vehicle. This system is also designed to assist your service technician in correctly diagnosing any malfunction. 2-57