Hey, so i needed to pass inspection so i removed my test pipe and put my oem cat back on, but i still have a cel, any ideas of how to make it go away?

 

You have to clear the codes. As far as I know, the CEL won't just go away by itself.

 

^^This. Just pull the back up fuse in the fuse box, wait a few seconds, put it back in and then start the car. The CEL should be clear and should stay off presuming your O2 sensor is working properly - link to DIY below.

https://www.s2ki.com/s2000/index.php...&t=549159&st=0

 

The CEL will go away by itself if a problem is fixed, but it has to finish a specific cycle to before it sees the problem is fixed.