GMC 2002 Envoy - Manual (Page 298)

5-14
How to Add Coolant to the Radiator
1. You can remove the radiator pressure cap when
the cooling system, including the radiator pressure
cap and upper radiator hose, is no longer hot.
Turn the pressure cap slowly counterclockwise about
one full turn.
If you hear a hiss, wait for that to stop. A hiss means
there is still some pressure left.
2. Then keep turning the pressure cap. Remove the
pressure cap.