Genuine OEM Audi Diesel Fuel Tank Cap, part number 5N0201550G. This cap is designed to securely seal the vehicle's fuel tank opening, preventing fuel evaporation, spillage, and contamination from dirt or debris. It features a convenient tether to prevent loss and is clearly marked 'Diesel' to ensure the correct fuel type is used. Using a genuine OEM fuel cap ensures a perfect seal, maintaining fuel system integrity and preventing check engine light issues related to evaporative emissions.