2004 Hummer H2 Owner's Manual - Page 344

If you get the overheat warning with no sign of steam, try this for a minute or so: 1. Turn on your heater to full hot at the highest fan speed and open the window as necessary. 2. If you're in a traffic jam, shift to NEUTRAL (N); otherwise, shift to the highest gear while driving - DRIVE (D). If you no longer have the overheat warning, you can drive. Just to be safe, drive slower for about 10 minutes. If the warning doesn't come back on, you can drive normally. If the warning continues, pull over, stop, and park your vehicle right away. If there's still no sign of steam, push down the accelerator until the engine speed is about twice as fast as normal idle speed for at least three minutes while you're parked. If you still have the warning, turn off the engine and get everyone out of the vehicle until it cools down. Also, see "Overheated Engine Protection Operating Mode" listed previously in this section. You may decide not to lift the hood but to get service help right away. Cooling System When you decide it's safe to lift the hood, here's what you'll see: A. Coolant Surge Tank B. Coolant Surge Tank Pressure Cap C. Engine Fan If the coolant inside the coolant surge tank is boiling, don't do anything else until it cools down. The vehicle should be parked on a level surface. 5-30