Genuine OEM Audi Fuel Vapor Line, part number 4K0201991BC. This hose is a critical component of the evaporative emissions (EVAP) system, designed to transport fuel vapors from the fuel tank or charcoal canister to the engine for combustion. It is located within the engine bay or underbody, connecting various EVAP system components. Using a genuine OEM fuel vapor line ensures correct material composition for fuel and vapor resistance, precise routing geometry, and secure connections to prevent leaks and maintain emissions compliance.