ok , I have a 99 RS with the R/T Hi-flow cat. I used it for about 6 months and didn't fix the CEL. But now I put back the stock cat on, I still get the CEL. I have restarted the ECU couple times, but still doesnt work. Could it be the O2 sensor is broken or something else?
thanks for any help
ED

 

What code do you get?

 

I didnt have the code read.

 

I'd do that, there's alot of things it could be. Autozone and most parts stores will lend you a scanner for a really low (or free) price.