1999 GMC Sonoma Owner's Manual - Page 119

yellowblue The anti-lock brake system warning light should come on briefly when you turn the ignition key to RUN. If the light doesn't come on then, have it fixed so it will be ready to warn you if there is a problem. Malfunction Indicator Lamp (Service Engine Soon Light) Engine Coolant Temperature Gage This gage shows the engine coolant temperature. If the gage pointer moves into the red area, your engine is too hot! United States Canada Your vehicle is equipped with a computer which monitors operation of the fuel, ignition and emission control systems. It means that your engine coolant has 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. The "Problems on the Road" section of this manual shows you what to do. See "Engine Overheating" in the Index. This system is called OBD II (On-Board Diagnostics-Second Generation) and is intended to assure that emissions are at acceptable levels for the life of the vehicle, helping to produce a cleaner environment. 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. This may prevent more serious damage to your vehicle. This system is also designed to assist your service technician in correctly diagnosing any malfunction. 2-61