Hi guys new to the forum. I'm purchasing a 2004 A4 1.8t Quattro and I need to replace the oxygen sensors, but I don't know if I need a 4 or 5 wire. It seems like I can't find both the upper and lower from the same brand with the same number of wires even though the guy I'm buying it from said they are both 4 wire. Help please?

 

they may be different. I think the pre cat one is 5 wire on a b6. Post cat is probably 4. I assume you can pull the plug on the fire wall and count the contacts. I'd be surprised if you need a rear one. Make sure you have read codes that say both sensors are bad.