2004 Chevrolet Impala Owner's Manual - Page 159

This gage shows the engine coolant temperature. It also provides an indicator of how hard your vehicle is working. During the majority of the operation, the gage will read 210°F (100°C) or less. If you are pulling a load or going up hills, it is normal for the temperature to fluctuate and approach the 250°F (122°C) mark. When the gage reads greater than 250°F (122°C), the HOT COOLANT TEMP light will be illuminated in the message center and a chime will sound continuously. If the gage reaches the 260°F (125°C) mark, it indicates that the cooling system is working beyond its capacity. See Engine Overheating on page 5-30. Your vehicle is equipped with a computer which monitors operation of the fuel, ignition and emission control systems. 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. Notice: If you keep driving your vehicle with this light on, after a while, your emission controls may not work as well, your fuel economy may not be as good and your engine may not run as smoothly. This could lead to costly repairs that may not be covered by your warranty. Malfunction Indicator Lamp Check Engine Light United States Canada 3-37