I've just installed a header on my 2003 Honda Civic LX, one from ebay. I went to Mufler man to install it, everything went well on the same day i drove it to work afterwards and everything was fine. The next day i went to workan stilleverything was fine. Then after work on the way home the engine light came on, no biggy I got home disconnected the battery for about 2 mins pluged it back in it worked fine. I went to my parents house which is about 25 miles away and the light has come back on.

So I hope that something isn't seriously wrong, my cat had to be taken out in the process.

 

ugh... I'd ask you to pull the code and see WHY your check engine light is coming on (because that's the right thing to do, instead of resetting it, and having no idea why it came on) but I can almost guarantee it's P0420... and that will stay on until you put your cat back in. is your O2 sensor just hanging there now or what?

 

^ +1 I too think its the cat since most of the new civic have 2 cat one called the main cat which is on the headers and one underneath the car. and most after market header only come with one opening for the o2 sensor which mean there an extra wire loose which would be the cat.

 

Actually there is two port for both wires that were on the stock manifold and cat. and both o them are connected, I was thinking of getting a aftermarket cat, but i'm not sure which kind to get and if the wires would stretch for enough

 

if theres a main cat up in the exhuast manifold and theres a sensor thats supposed to take a reading from it, and its just taking a reading of the exhaust as it flows thourhg hte header, you'll get a cataltic converter efficiency CEL.

 

If i was to get a o2 simulator, would that fix the problem. or if i got a new cat. I'd have to extend that wire a ways.