well im not that technical on what it does..... but i believe it senses the exaust and adjusts the fuel curves accordingly thru the computer....
its preaty important....
a bad O2 sensor can kill your gas milage very easily!!!!

 

oh ok , well thanks for the helping a 17 year old semi-newb out lol, i guess ill do some more research on the headers and ifguire out wut im going to do

 

dude theres nothing to it, I get my headers in about 3 more days and all you have to do is jack the sucker up remove the bolts out onthe new one, and of course put on the bolts again....lol but yeah I'm worried about the CEL too, that's why you buy an O2 Simulator, type that in ebay "O2 Simulator civic" and it'll show up. it's like 5 bucks and 5 shipping 10! lol