Hello fellow tech-savvy Honda enthusiasts, Ive got here some data from my Ho2s. Ive got the p0420 code, as well as an evap canister small leak code. After trying to figure out my evap code, doing some vacuum and solenoid testing etc. i cleared the code, and when it came back, it was accompanied by this p0420 code. Here is a screenshot i took from driving around for a bit at temp.
Now, from everything that ive read, the secondary Ho2s should be pretty consistent, which of course it is not. And the upstream Ho2s should be a nice smooth sine wave, which it doesn't seem to be either. They seem to mimic each other. What bothers me was that this happened all of the sudden. prior to this, there was no problem. So i am calling upon the catalyst specialists of honda tech for your opinions. am i doomed to spend the cash on a new converter? The previous owner installed an aftermarket header and full stainless exhaust. The upstream Ho2s has the standard honda connector i recognize from my old civic but the downstream sensor has some strange plug dealy you have to connect each wire individually. Could an incorrectly attached wire cause this? wires in the wrong spot? All opinions are welcome. Car is an 00 Civic Si-G EJ8 D16Y8. Thanks in advance!

 

Bump

 

Post pic of secondary sensor.
PM me and I can help you further.

 

Did the previous owner even install a converter, or just an empty pipe?

 

Top graph is bank 1 sensor sensor 1 (upstream), bottom graph is bank 1 sensor 2 (downstream). Unless im doing this wrong? Im having a hard time believing that it went from being just fine, to like its not even there in a matter of one night.