Saturn 2007 Relay Owner's Manual page 389

You can run the engine to keep warm, but be
careful.
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 your exhaust pipe. And check
around again from time to time to be sure
snow does not collect there.
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 charged.
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