2006 GMC Savana Van Owner's Manual - Page 224

{CAUTION: Snow can trap exhaust gases under your vehicle. This can cause deadly CO (carbon monoxide) gas to get inside. CO could overcome you and kill you. You cannot see it or smell it, so you might not know it is in your vehicle. Clear away snow from around the base of your vehicle, especially any that is blocking the exhaust pipe and/or the fuel operated heater exhaust system, if equipped. And check around again from time to time to be sure snow does not collect there. If your vehicle has a diesel engine and a fuel operated heater, see "Fuel Operated Heater (FOH)" in the diesel engine supplement. Open a window just a little on the side of the vehicle that is away from the wind. This will help keep CO out. Run your engine only as long as you must. This saves fuel. When you run the engine, make it go a little faster than just idle. That is, push the accelerator slightly. This uses less fuel for the heat that you get and it keeps the battery (or batteries) charged. 4-28 You can run the engine to keep warm, but be careful.