I keep getting these codes below:

16518 P0134 O2 Sensor Circ.,Bank1-Sensor1 No Activity Detected
17521 P1113 Bank1-Sensor1 Internal Resistance too High
17866 P1458 Exhaust gas temperature sensor 2 short to ground

I replaced the upstream O2 sensor twice and got the 16518 code back on shortly after replacing the sensor. The other codes eventually come up. Audi suggests changing the O2 sensor again + replacing the catalytic converter. Does it make sense that a bad catalytic converter keeps making the upstream O2 sensor go bad?? If there is no activity in the upstream O2 sensor, wouldn't that make sense that it is causing the cat to read bad? Wouldn't the downstream O2 sensor go bad if the cat was bad?

Just looking for some comments or advice if anybody has experienced a similar problem before I have the catalytic converter replaced.

 

Well since you didn't list what car you have im gonna assume its a 2.7T.
You need to replace the Before cat O2 sensor on the PASSENGER'S side which is bank 1, i can only guess that you were replacing the drivers side one? You don't need a new cat, thats rediculous. You may need a new EGT sensor, but your code doesn't say which bank its on. EGT sensors can cause all sorts of problems.

 

It is a 2001 A6 2.7T. It is the O2 sensor on the PASSENGER side that has been replaced a couple of times, code comes back on immediately. Thanks for the info, I'll look into the EGT sensor replacement and let you know.

 

Shouldn't do that, regardless you won't need a cat. You may have a pinched wire in the harness to that O2 sensor, which would be a real bitch to fix in that case....