GMC 2002 Yukon Denali Owner's Manual page 275

5-16
1. Park the vehicle on a level surface. You can remove
the coolant surge tank pressure cap when the cooling
system, including the coolant surge tank pressure cap
and upper radiator hose, is no longer hot. Turn the
pressure cap slowly counterclockwise (left) about
one full turn. If you hear a hiss, wait for that to stop.
A hiss means there is still some pressure left.
The coolant surge tank on
your vehicle may be
equipped with one of the
two caps shown.