Hello
I have a 96 civic hatch and my CEL came on. Went to go get it looked at and it came up P0420. Noticed it said P0420 Catalyst System Efficiency Below Threshold (Bank 1). Funny part is i don't think it have a catalyst on it. I have a D16y7
It goes header -> stock exhaust system -> aftermarket muffler. I don't think i have one b/c when i changed out my sub-frame i just detached the header and pipe.
Don't think its that so was wondering could it be my o2 sensor b/c it also says thats leaking. and also something about my A/F ratio concern. and ignition concern but it starts fine.
Any help would be good. i read around and found something about a accord didnt think it would be the same for a EJ6.

 

Does the manifold look like this?

 

Nope

 

Then you probably have no cat based on the info in your OP. That will cause a P0420.

Where is the secondary 02 sensor?

 

I just know there is one on the header and thats about it. don't know where the other is atm. haha but it has been off for a long time so y would it just kick on out of nowhere