Hello all.
I have a 2000 A4 2.8 ATQ 2wd 5 speed, and recently re-did both heads, and all 4 O2 sensors. Granted the sensors were local universal auto part sensors. So to get to my point, I got a CEL soon after I got the car running. It was for both banks having the Cats below threashold. Both sides. If it was just one side, I would have guessed it could have been a CAT. Therefore I would have swapped the post cat O2 and see if the code followed. Since it was both sides at the same time, could it be a computer thing? I have re-set the code now 3 times, and the same code keeps coming back. I really don't want to go to the stealership to get my car tested for $150 and find out it is something simple. If you have any ideas, please post.

Thanks,
Andy

 

Only thing that really would pop out would be to doublecheck that the post-cat O2 sensors are wired correctly - make sure that none of the wires pulled loose at your connections and that the wires are properly connected. Also be sure the sensors (all four) are good and tight in the pipes and aren't leaking air that could throw false codes.

Have you cleared the codes to see if they come back, indicating a genuine problem and not a ghost?

 

Have you tried swapping the old post cat 02 sensors back in?

 

Would poor gas cause this CEL?
To start it off, the other day (Friday) I went to start the car and the CEL was OFF. Drove around for an hour or so, and on the way home, it came back on. Rest of weekend, it stayed on. I filled up with premium gas yesterday, and CEL was still on. Drove kids to school, still on. Went to work today, and after I stopped at the store, the CEL was OFF again when I started it up.
The only thing I can think of is the gas. If not the gas, then probably the computer. Hopefully someone has dealt with this and can give me some help.

Thanks,
-Andy

 

I will check this too. I guess loose wires would also cause this, but it has the good weather-proof connectors. Worth a shot though.