Hello honda community. I am a seasoned honda user/mechanic and Ive done many many swaps and all that, but this one is just downright a stumper. I have a 2000 DX sedan, CA emissions. Recently, I purchased a d16y7 to replace the engine. I am now getting a p0420 code, for the catalytic converter. I've done the 02 sensor voltage tests and they say the cat is working properly. Also, the light comes on like clockwork when reset, basically exactly 20 miles after shutting the light off. The only things I can think of is possibly the engine i got is Federal emissions, and I may need a different ECU, or the engine i got was a 96-99 engine, and I need an ECU, as ive been told that 96-99 are different than 2000. Please any help would be greatly appreciated!

 

An exhaust leak can also throw P0420. You might want to look into that.

 

I feel that the exhaust leak would throw the code slowly though..and maybe not within the exact same time period. With my CEL experience, this seems like its almost programmed to come on at the same time..which i know it obviously isn't, but it just feels electronic to me. It would have to be a relatively good size exhaust leak to throw that code correct? The exhaust sounds quiet, so if there is a leak, its VERY small and basically un-noticeable..Any input on the ECU part of it?

Recently discovered..The car is obd2b and the engine was in fact obd2a, at least that's what i was told because the distributor plug of the new engine was rectangular instead of square, so I used my old distributor. Dont know if that changes anything, but any help would be great!