I had a header and high flow cat installed on my 97 civic ex. The new o2 bung is in the downpipe not the converter. Now my check engine light keeps coming on and the message it gives is tha the cat isnt working. Even if i have a new whole blown in the cat i think it will still say that because its high flow.

the search is your friend
link (http://www.automotiveforums.com/vbulletin/showthread.php?t=321974&highlight=high+flow+cat)
this has been covered before

because you need one in the cat ;)

:iagree: either u dont have an o2 after the cat...or u didn't plug it in...