2004 Chevrolet Colorado Owner's Manual - Page 160

Engine Coolant Temperature Gage This gage shows the engine coolant temperature. Malfunction Indicator Lamp Check Engine Light Your vehicle is equipped with a computer which monitors operation of the fuel, ignition and emission control systems. If the gage pointer is near the top of the gage, the engine is too hot. 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. See Engine Overheating on page 5-28 for more information. 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 check engine 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. 3-32