Well guys the CEL is still off and running great. 750 miles. Hot weather, start stop etc. 9500rpms and running just fine.

 

Well I'll be damned...

 

Just so I'm clear on what you did: You took a new upstream O2 and put it in the downstream port and plugged it in and that's it?

 

I'm one of the fortunate few that my P0420 doesn't go off often. In fact it hasn't this year ever since I changed to a different mid-pipe (bung relocated further down). But this seems to be a good long term solution.

 

I took a failed up stream O2 sensor and put it in the downstream bung. NO CEL for almost 800 miles.....

 

Is it plugged into the wiring harness anywhere? I'm trying to noodle out *why* it works. Is it simply a matter of something O2 sensor shaped being in the hole or is there some sort of signal being sent to the ECU.

 

I took a failed up stream 02 sensor and put it in the downstream sensor position and connected the wiring. Simple. Try it cuz it works. So now I have a new 02 sensor in the up stream position and the failed up stream 02 sensor in the down stream position. Don't make any harder than it is. NO CEL and NO Code after 800 miles.

 

What's weird about that is the front O2 measures current while the rear O2 measures voltage. It would be a heck of a coincidence for the ECU to be getting the right voltage responses from the broken front O2 sensor as it expects from a functional rear O2 :o

 

Yes, Loki, you have hit on what I'm driving at. What is the failed O2 sending to the ECU to make it happy? If we know that it becomes a duplicatable solution.
Otherwise it's just a gamble that one can lay hands on a failed O2 sending something that will make your ECU happy.

 

can you try it with a good upstream O2 sensor? I think it is easier to find working condition ones than verified failed upstream sensors. This is an intriguing topic.

Gawd, we must've ran out of rx8 topics nowadays. Oh! Ice cubes!!!!!

 

9/6/2020 still no CEL....!! running just great.

 

I don't know if it requires a failed 02. The downstream sensor is different than the upstream. Try it with any up stream 02 sensor and see if it works. I have over 1000 miles and still no CEL....
al