Hey guys I just had to replace my Cobb dp because the flex pipe on it somehow broke and since Cobb no longer makes a dp I replaced it with a whoosh one because it was only $300. Originally went to an exhaust place to get a hanger fixed but found out the dp was broken but no code(the car did idle funny sometimes on cold starts think back on it). I did get a p0420 after leaving the exhaust place but I think because the guy mess with it to show me and that triggered it. After about two weeks of driving on it, I ordered a new whoosh catted dp and got it installed at the same place but the code was still there and the dude didn’t say anything. I was thinking the 02 senser just went bad from me driving on the bad dp for a while or this catted dp just trips the 02 (which would blow chucks cuss it cost me a shit ton to replace). Idk tho any opinions would be greatly appreciated 
and if you know of an good shops in south jersey or Philly let me know
You’ll need to use a defouler on the second O2 sensor to prevent a P0420 code.
The cat in that downpipe doesn’t clean the exhaust as effectively as the OEM one, which is triggering the code.
It’s a little spacer with a flow restrictor, and it tricks changes the nature of the exhaust flow over the O2 sensor.
Damn thanks. I’m probably going to replace both 02 sensors and get a defouler. I just hope my car passes inspection next year.
No need to replace the sensors. The code doesn’t mean they are bad, it means they are working and reading out of spec. Just get the defouler installed on the downstream sensor.
Ok, any defouler recommendations? I found a couple on whoosh’s website might go with the J Style one.
They work somewhat okay when they’re warmed up, but when they’re cold, they barely do anything, which is when the CEL gets triggered. I can actually smell the difference once it reaches temperature in my car, lol.
Defouler bro, will never worry about p0420 again