awdinut

I saw a video on you tube that showed how adding an O2 sensor extender to the down stream sensor reduced the amount of sensor exposed to the exhaust gasses to successfully extinguish the CEL. I would love not to have to look at that CAT induced CEL in my car. What I dont know is whether or not the down stream sensors on a 6.0 are accessible enough to add the extenders....any thoughts ?

MP4.2+6.0

I can't answer on post cat sensors, but maybe indirectly I sort of can...

I never had any post cat sensor issues bottom line. As in, are you sure? That is, you have codes specific to (only) post cat sensors? Or maybe you have combination codes with pre cat sensors? If those, my experience is typically change the pre-cat and it is done. All four pre-cat W12 sensors can be accessed with patience and the correct tools under hood. I posted on it in past.

Also, check the old W12 TSB on O2 sensors. Only went thru 2005 IIRC, but I paid attention to it. The one issue I had other than normal repair and replace was a failure of the wiring harness on one O2 sensor BEFORE the connector--as in, on the "car" side of the harness. Again, I have an old post on it. You get a new connector from Audi, some pre-wired jumpers with the tiny bugger end connectors already crimped on, solder them in with Tyco connectors, push new wire terminals into connector, and good to go. You will find the small wires used throughout the O2 connectors on harness side are pretty small. Only the heater wires for the pre-cat sensors are decent gauge. I suspect over the years and with some service abuse, the little ones could get compromised internally.

See this old post. It gets into those Tyco connectors and my own experiences. https://www.audiworld.com/forums/a8-...ifold-2867390/ It also has some W12 pics OUT of the car. Notice those post cat sensor cables. They really aren't near really hot stuff, and also why I wondered if you are really on the right track with.your issue. What does get hot and fried from exhaust and cat temps are the exhaust side cam sensors at back of heads, and maybe the coolant sensor on back side of (USA) driver's head. Other posts on those.