I have a 2000 eclipse GS and my check engine light came on recently. I have headers, a catback, and a CAI. I already had the catback and the CAI on my car then I installed the headers. Thats when my engine light came on. I took it to autozone and had it read and they said it was a catalyst system efficiency below threshold. So I replaced my front O2 sensor and disconected my battery to reset the computer. The engine light came back on though. Any advice on what I can do or what it might be? Thanks

 

if it was the o2 then it would have come up with that code. I think the reason for it may be the increase in air flow with the header. Your Cat may not have been working too well before the headers and now with it, it is alittle worse. So it might be that the cat is bad.