Keep the check engine light off with MagnaFlow OEM Grade Federal/EPA Compliant Direct-Fit Catalytic Converter 49918. With features including free-flowing mandrel-bent tubing and highly corrosion resistant stainless steel construction easily install this spun body converter yourself using the proper tools no cutting or welding required. MagnaFlow's state-of-the-art metrology department uses the latest 3D scanning systems during research and development so you can be confident that your new part will fit and function like the original equipment. By replicating the OE spun body design the single laser fusion weld greatly reduces the possibility of a leak and our compact low-mass design also allows for greater thermal efficiency. This direct-fit catalytic converter is designed specifically for the 2004-2009 Audi S4 and interchanges with OE parts 8E0 254 554 QX and 8E0 254 551 QX. This replacement part is designed to meet or exceed Federal emissions requirements set forth by the EPA complying with legal standards for OBDII Federally registered vehicles with California or Federal/EPA Emission systems.