?2pcs Upstream for 02- 2004 Audi A4 3.0L 02 Oxygen Sensor Air Fuel Ratio O2

Compatibility: 2002-2004 Audi A4 3.0L 2002-2004 Audi A4 Quattro 3.0L 2002-2004 Audi A6 3.0L 2002-2004 Audi A6 Quattro 3.0L 2003-2005 Audi Allroad Quattro 4.2L 2004-2009 Audi S4 4.2L Q&A: Q:What is Differences Between upstream and downstream O2 Sensor? .