2008 GMC Sierra 1500 Pickup Owner's Manual - Page 340

If there is still no sign of steam and your vehicle has an engine-driven cooling fan, push down the accelerator until the engine speed is about twice as fast as normal idle speed for at least five minutes while parked. If there is still no sign of steam and your vehicle has an electric cooling fan, idle the engine for five minutes while 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" later in this section. You might decide not to lift the hood but to get service help right away. Overheated Engine Protection Operating Mode If an overheated engine condition exists and the ENGINE POWER IS REDUCED message is displayed, an overheat protection mode which alternates firing groups of cylinders helps prevent engine damage. In this mode, you will notice a loss in power and engine performance. This operating mode allows your vehicle to be driven to a safe place in an emergency. Driving extended miles (km) and/or towing a trailer in the overheat protection mode should be avoided. Notice: After driving in the overheated engine protection operating mode, to avoid engine damage, allow the engine to cool before attempting any repair. The engine oil will be severely degraded. Repair the cause of coolant loss, change the oil and reset the oil life system. See Engine Oil on page 5-13. 5-28