Just checked for codes...and i get 17522 which is the rear o2 sensor on the cat. i clear it and it comes back. i know its just the sensor that tells the ecu if the cat is working properly or not. Does this effect performance? and how important is it to have working properly?

 

As far as I know, the rear one is just a sniffer that tells you about the cat's efficiency, doesn't affect anything. The front one is the one that reads the A/F ratios. I used to get a cat insuficiency code with my HFC, I haven't had one since I did this:
http://www.audigeeks.com/forums/index.php?topic=2167.0

 

The rear O2 sensor malfunctioning won't affect performance in any way, but it will make you fail an emmisions test. Plus you don't want to have a constant check engine light because if something else goes wrong the light will already be on and you might not know that something else has gone bye bye.

 

well i have a Test Pipe and the revo software eliminates the CEL that comes on, but it still logs that the o2 is bad. would that still pass emissons?

 

I think the law is if it has two or more stored codes or the cel is on its an automatic fail.
So if you can get the cel off and only have one fault code in the ecm you should pass. But laws change from state to state so i don't know.