Keep the check engine light off with MagnaFlow OEM Grade Federal/EPA Compliant Direct-Fit Catalytic Converter 51664. With features including free-flowing mandrel-bent tubing and highly corrosion resistant stainless steel construction, easily install this 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 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 to fit the 2000-2004 Audi A6 Quattro 4.2L & 2002-2003 Audi S6 4.2L. MagnaFlow 51664 interchanges with OE parts 4B3 253 058 AX, 4B3 253 058 BX, 4B3 254 550 CX, 4B3 254 550 GX. 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.