Hissing Sound When Removing Fuel Cap
WARNING: This page does not describe the selected car, but rather 32 other vehicles, including the 2002 Mercury Sable, 2002 Mercury Mountaineer, 2002 Mercury Grand Marquis, 2002 Mercury Cougar, and 2002 Lincoln Town Car. However, it is still accessible from the selected car via links, so may be relevant.
For diagnostic procedures, see HISSING SOUND WHEN REMOVING FUEL CAP symptom under SYSTEM TESTS (EVAPORATIVE EMISSION) in SYSTEM & COMPONENT TESTING - EEC-V - GASOLINE article.