Before I start I have done some research. I do have a question about something though hence why I'm creating this post. Bought the LX almost a year ago and drove it for several months with a leaking driver side exhaust manifold. It was leaking quite a bit. Never got a cel for it though. Finally got around to replacing it. When I took it off I couldn't get the old o2 sensor out of the manifold so I replaced that as well. Within a week I got the p0420 code. Since I already replaced the upstream sensor I went ahead and replaced the downstream sensor. Code went away for a few days then came back. I purchased this sensor from amazon but it is supposed to be an actual denso sensor. Both of them are. So, for the last few weeks the cel has been coming and going. Last night finally though I was able to hook my scanner up to it. The bank 1 down stream is definitely registering lower numbers than the bank 2 downstream sensor. My scanner also had a question mark next to the b1s2 sensor. I'm just really trying to keep from spending $1200 on a cat. It doesn't rattle or even have hardly any rust on it. I checked for exhaust leaks last night but couldn't find any. This afternoon my plan is to clean the maf, swap the downstream sensors and hopefully figure this out. I know there is the possibility of a bad gas cap as well. This rig has 450k miles on it so I know there is the possibility of a bad cat but is there anything else that I'm missing?
Thanks
Thanks