So, hi, my name is Jessica I'm new to this forum so bear with me if I make mistakes.

I own a 2001 eclipse gs, 4cyl 2.4L. It's a little old with 120K on it so this might be one of the reasons why I am having so many problems. Recently I installed a header on it, everything went smoothly and it ran great but then everything went south. First it popped up P0134 which read "O2 sensor circuit - no activity detected" so I replaced that and the code when away. Then it popped up P0421 which reads "catalyst efficiency below threshold bank 1". I'm not sure what to think of this one, I changed out a bad gasket hoping there was a leak, but that wasn't it and it also wasn't the bad O2 sensor. I have also been having my oil pressure light flicker on whenever the RPM is below 500 or at idling speed. There has been no difference in drivability that I have noticed so I'm just looking for any advice anyone has to help me troubleshoot.

I appreciate any answers, Jessica

 

The p0401 is a a cat converter efficiency code, the cat probably took a crap.