02 sensor connectors are the big brown/gray/black ones. If an 02 sensor is the culprit, then it would be more likely the pre-cat sensor and not aft-cat one. In this instance, I believe it's the big (wide) black one under the passenger-side mounting tab, in your thumbnail.

 

wow i am completely lost... i was hoping to trace the O2 sensor by the cable, but that is not helping. Where exactly is the O2 sensor? Is it below the coolat thing, back side of engine(towards windshield)??
Any help would be appreciated...
Thanks
--d3

 

Yeah, the sensor is sticking almost straight up out of the driver's side exhaust pipe. If you go back to your picture for reference, it would be right below where the mounting hole is in your coolant reservoir. The passenger front one is in the same location but on the passenger side exhaust pipe. The rear sensors are both underneath the car and just behind the cats. Sorry, that I don't have a picture for you. The wiring connector was the one mentioned earlier. Audi didn't produce separate sensors for passenger or driver. They're interchangeable and that's why (excessive cable to accommodate the passenger length) the driver's side cable goes toward the shock tower then back to the sensor instead of straight to it. Maybe someone's got a picture to help you.

 

I will try to get a better look at it today when i go home. Also, i am assuming the driver side one is the pre-cat sensor?
Thanks
--d3

 

So today while driving to work i got my check engine light on. Came home ran vag-com and got another code now

17537 - Fuel Trim; Bank 2 (Mult): System too Rich
P1129 - 35-00 - -
NEW ONE :17535 - Fuel Trim; Bank 1 (Mult): System too Rich
P1127 - 35-00 - -

Does this mean that my post-cat sensor is gone also now? Couldnt find this code on wikiross website...BTW, i havent changed the pre-car sensor yet, it is getting changed next week when i get my TB and tirod ends changed. Thanks for the help

--d3

 

Sounds like its your precats, I had/have the same problem with my 2.8, I only get 250m per tank, mostly city though. I get the same codes every few months or so. There are a few ways to check the O2 sensors and its a pita to change them too. You can check them by reading the ohms like in the article posted below or reading the voltage output with the car on. I don't remember the threshold number right now, read the bentley manual for the instructions for that. Or if you can get it on a VAG and it'll tell you the threshold numbers for the maf also that way you can tell exactly wheres the problem. This info might help...

http://www.audiworld.com/tech/eng101.shtml

 

So its just my pre-cat O2 which is causing these codes?
I wanted to change the O2 myself, but its been so cold out lately that i just told the stealership to change the o2 (450 bucks) ... I hope i dont have to change the post-cat O2 also, that will be another 450 lol

--d3

 

wow that article was helpful, i didnt know my 2.8 has 2 pre-cats and 2 post-cats, i just though it has 1 pre and one post. With that color coding, i also know where they are...
But one question trey, i dont get a faulty heater code like it shows in article?? When you had those codes, what did you do? Did you change both pre-cats?

--d3

 

I didn't do anything yet lol I'm waiting till the winter ends.

 

lol i want to change it myself and save some cash, but everyone seems to say its pita ...
hopefully a tech reads this and helps me