Checking fuel supply and tank ventilation systems for leaks: Avant:

WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2004 Audi A6, 2003 Audi S6, 2003 Audi A6, 2002 Audi S6, and 2002 Audi A6. However, it is still accessible from the selected car via links, so may be relevant.