Cadillac catera 2001 Benutzerhandbuch

1. 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) until it first stops. 
(Don’t press down while turning the pressure cap.)

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 slowly, and

remove it.