just bought my 09 ralliart and the 02 sensor is making the check engine light come on . the guy that had it before me put a high flow cat on it .he said this is what is making the ck engine light come on and get code saying it is running lean. is there any way to bypass the 02 sensor ? if so any help would be great.

 

Get it tuned and that will go away :P

 

it has a tune by jestr tunning in orlando

 

Need more info:
You said it had a hfc, does that mean it no longer does? Is it now stock?
Talk with Jester, as they will know how it was set-up. For instance on my car I've spliced into the rear o2's signal so I can log with my UEGO through the Tactrix. BUT...I left the stock sensor in there to plug the hole, and its not being used. That means if I were to go back to the stock cat, I would get a CEL because the stock 02 is covered in carbon and would no longer be producing a usable signal (causing the ECU to say 'what the hell' and throw the CEL)
That is just one possibility of about a dozen...NEED MO' INFO

 

Pull the code man, OBDII is a wonderful thing when people pull the freaking codes

Most likely scenario is you have a cat inefficiency code (because of the high flow cat) which has nothing at all to do with running lean... which again... would be verified by pulling the codes.

 

code was pulled it said running lean and 02 sensor. can i just unplug the sensor and run a jumper or will that screw things up?

 

No you can not. Be more specific with code# please. P0171 for lean? P0134 for O2? What mods are on the car? I've seen a poorly (or never been) scaled MAF sensor throw both those codes (on my own car for example)

 

That is not what the code said, that is someones interpretation of what the code said.

As Chi-Town said, post the specific code #'s