I have spent a number of hours searching for an answer to my issue but have come up short. I VERY recently purchased my first Audi, a 2006 2.0T Quattro with 117K on it. It came with a CE light which I scanned and came up with O2 Sensor Circ. Bank1-Sensor1 slow response as well as Catalyst System Bank1 Efficiency below threshold. Now I figure the 2nd code is a result of the first code so no problem, I can see the O2 sensor right there in line after the turbo so lets swap it out! Looked up online and purchased a Bosch 17480 listed as upstream and brought it home. Proceeded to unlatch the "Black" square type connecter and followed the line back and it ended up going to the downstream O2 sensor that is after the cat closer to the firewall. So my question is did the previous mechanic inadvertently swap the two sensors. Following what should be the upstream to the connector showed me a flat type connect that is dark reddish in color, shown in the parts catalog as a downstream O2 sensor. It seems like my sensors are reversed in their respective positions in the grand scheme of things. Would the car even run like that? OK. Thats rhetorical as it is running, just with a CE light.

Thoughts and advise please.

Thanks for your time and interest……

RDW

 

If they were reversed I could see that causing an issue. It would run but because of the backward readings it would trip the CEL. I think if you got them connected back up right order it should be ok. Be sure to clear the codes or, better yet, disconnect the battery as to reset the ECU to forget all those "bad memories" and give it a fresh start.

On my A8, the after-cat O2 sensor connectors are under the carpet in the floorboards just in front of the seats. The before-cats are on the firewall. Kind of hard to get them crossed up.

 

Dave,

Yea, on my A4 at least, both of the connectors are located at the firewall on the drivers side, in close proximity to each other. In fact, on the pipe they are maybe 12 to 18 inches apart, upstream just north of the cat and downstream just south. Since both of the leads run behind the engine, I can possibly see the two getting crossed up especially if the tech installed them in reverse locations to begin with. The difference between the two is upstream seems to have 5 leads while downstream seems to have only 4. I need to get the stubby 22mm line wrench or the open tip crows foot socket to remove the downstream, kinda tight down there and will just swap them to begin with to see if that clears the issue. I will have to say that even with the CE light, this vehicle is very satisfying to drive!

 

Ok. Got out there after work today and swapped the two O2 sensors. Upstream sensor is where it belongs and the upstream is where it belongs. Put 50 miles on the car and it did not trip a CEL. Before when I would clear the CEL would come on within 10 min of driving, so hopefully this will close the case!

 

Yep.. I think you've got it licked now.. Nice job...