So I have been running with a p0420 code for a few months with my emissions (CT) overdue, and they finally got me to come in by withholding my registration renewal. After troubleshooting and even trying the non-fouler trick, I couldn't get rid of it. So in my research, I learned that CT allows 1 or 2 monitors to be not ready and still pass (assuming no stored codes). In doing my troubleshooting, I noticed on my OBD reader app that the cat monitor was always the last to be ready, and that it would not come on until doing the 55 mph portion of the driving cycling (all the other monitors came on with local non highway driving.). So I reset my CEL, drove under 55mph until all monitors were ready except cat, and got the emissions passed. I am not sure what other parts of the driving cycle trigger the other monitors exactly, but I wonder if this could be done to bypass other codes if emissions are due?

 

Thats an easy one. Buy a new o2 sensor and I THINK bank 1 precat. Not cheap...but a permanent solution. Shortcuts never work out in the end.