2004 GMC Sonoma Owner's Manual - Page 270

Radiator Pressure Cap Notice: If the pressure cap is not tightly installed, coolant loss and possible engine damage may occur. Be sure the cap is properly and tightly secured. {CAUTION: Steam from an overheated engine can burn you badly, even if you just open the hood. Stay away from the engine if you see or hear steam coming from it. Just turn it off and get everyone away from the vehicle until it cools down. Wait until there is no sign of steam or coolant before you open the hood. If you keep driving when your engine is overheated, the liquids in it can catch fire. You or others could be badly burned. Stop your engine if it overheats, and get out of the vehicle until the engine is cool. Notice: If your engine catches fire because you keep driving with no coolant, your vehicle can be badly damaged. The costly repairs would not be covered by your warranty. Engine Overheating You will find a coolant temperature gage on your vehicle's instrument panel. See Engine Coolant Temperature Gage on page 3-28. If Steam Is Coming From Your Engine 5-26