Fuel Evaporative System
WARNING: This page is about a different car, the 2002 Audi S4. However, it is still accessible from the selected car via links, so may be relevant.
When vehicle is not in operation, an EVAP (charcoal) canister stores fumes produced through evaporation in the fuel tank and other related system components. During engine operation, fumes are purged from EVAP canister and consumed in the combustion process.
To test EVAP emissions system, see EVAP emissions system related DTC(s) under DIAGNOSTIC TROUBLE CODE DEFINITIONS in appropriate SELF-DIAGNOSTICS article.