02 sensor and cat conv. Questions

I pulled the P0420 code a couple months ago and had it checked out at the mechanics shop. I was told that the rear O2 sensor and rear cat converter were not working properly and that was why I was getting the P0420 code.

So, it's around 2 months later and I'm able to buy the parts. I'm debating if I should buy both 02 sensors (upstream and downstream)? And I'll be replacing the rear cat with a magnaflow 50 states.

1. Should I buy both sensors even though they said the upstream seems to be working properly? (That was 2 months ago)

2. I'm guessing its possible for the front cat to have gone bad between then and now. If I buy the upstream O2 sensor, and the upstream cat has gone bad, will that make the "Newly replaced O2 sensor" go bad?

3. Would driving for 2 months on a bad rear cat and bad rear O2 sensor make the upstream cat and upstream O2 sensor go bad as well? Or could it make one or the other go bad/ not work properly?


All in all I'm trying to figure out if I should wait to replace all these parts at the same time, or if its ok to replace what I can now, then when I get more $, replace the rest. I'm also worried that since I have been driving with a bad rear cat and 02 sensor for two months that maybe it ruined the upstream cat and upstream O2 sensor also?

I read awhile back that since all this stuff is connected, if one goes bad then the others start to fail. So that's why I'm worried I may have waited to long and now I need to replace both cats and both 02 sensors. Which I can't do because these parts are not cheap!

Hopefully I can replace just the downstream cat and sensor and call it good! Let me know what y'all think

 

*BUMP* I'm having the exact same dilemma. Was your question ever answered?

 

Hey, it wasn't really answered but I did some research and ask around a couple different reputable muffler shops. I ended up getting magnaflow cats for the front and rear. Also got the denso air flow sensor (connects to front cat) and denso O2 sensor which connects to the rear cat.

My reasoning was just to get everything replaced and all has been fine ever since (about 1.5 years). I didn't go OEM cats due to the price but after the many many good reviews on the high quality cats that magnaflow produces I decided on those. You don't need to get California emissions cats but there is another term for the cats that do fit and work well with our trucks. Best in mind they are not cheap but way cheaper than OEM cats. Plus I got the OE fit models that's way I could remove and replace the old cats with the new. It was super simple because of the high heat temps those joints are under but it took lots of grease to lubricate the bolts the replaced and all is fine. The sensors are simple but do suggest lubricating all the nuts and bolts about a day before use. Hope this helps. Let me know if you have any questions

 

Thank you much for the quick response! I do have a couple more questions though... Since I'm in TX, would it be possible to replace both cats with one Magnaflow obdII direct fit one? I have already replaced both sensors with denso's and the code just recently came back a week ago. My trucks due for an inspection and I have an AeroTurbine 2525xl thats been teasing me since Xmas. If its an absolute must to replace both cats to prevent that dang code, I'll do it... Works been slow, so money's beginning to wear thin.

On a side note, I was researching this and came by a thread where one dude used 2 non-fowl sparkplug adapters to move the sensors? Have you ever heard of this?

Edit: By the way, you got one clean Taco man!

 

Never have heard of the spark plug adapter jig to replace the sensors but it's worth a shot if you want to go that route. I was told by many that the front cat rarely "goes bad" and the AF sensor replacement should be enough. As for the rear I'd suggest replacing both the downflow cat and the O2 sensor. But again I had mine tested by a reputable shop but I ended up changing everything since I had the $ at the time. I've heard too many stories of people going the cheap route and it only lasting a month then the codes pop back up. I'd stay with the denso sensors you put on and since they are new they should be good to go. Maybe just replace the rear downflow cat and see where that gets you. I'd suggest using a good quality cat though. If magnaflow is still too pricey try rockauto, they had a couple of high quality cats that would work for our trucks

 

Would I need a would I have to use the CARB complient option to not throw a code? I've replaced both sensor's, so I'm almost positive its a cat. My trucks got 265xxx miles on it so I'm also thinking I'd might as well just replace everything as well... What I'm really wanting to know is if I could get away with just one bad ass cat and a straight pipe on the other?