P0420 Code after replacing the front O2 Sensor

[2002FO]

OK, I normally don't post on topics that have been beat to death, but I searched, and I just want to verify what I've come up with.
I purchased an El-Cheapo Pre-cat O2 sensor on eBay when I started getting the P0134 code on the original sensor. It lasted probably 3 days and the code came back. I drove it like that all summer until I finally had enough of resetting the SES light. After doing some research, I learned that the Denso is the sensor of choice, so off to Rock Auto I went.
Fast Forward to this morning.... I fixed the P0134 code just like that (making snap sound with fingers...) with the install of the good quality sensor.
Now, I'm getting a code P0420. The cat is probably 2 years old with maybe 18K on it. I did replace the rear sensor back in the spring, before I started getting trouble codes on the front sensor. I'm pretty sure it's a.......Bosch ...

I know, I know... But I didn't know then. So just to verify, I'm fairly confident that the rear Bosch sensor is acting up trying to communicate with the Denso pre cat sensor...

Time for another Denso for the rear sensor.....

Your thoughts????

[justdave]

Signal levels get sent to the PCM; sensors do not communicate with each other. UN-fortunately, when you decided to drive around with an inoperable (and illegal) Emissions System, you very likely killed your Catalytic Converter's very thin layers of very expensive internal coatings. Running an engine with incorrect fuel/air ratios (without WORKING 'oxygen' sensors, your PCM is trying it's best to do an impossible job), will destroy most of the honeycomb of any 'Cat' within weeks; it will never be the same as new/good-used again, and will just keep limping along. Take it to a professional repair shop is the best advice in this case.

[2002FO]

New Cat then, huh... Time to break open my sons piggy bank...
So, with all this talk about Bosch sensors, how do I know it's not just the sensor? And the Cat is that sensitive, that the A/F mixture would ruin it that quickly? I've noticed no problems with fuel efficiency (avg 23/32 mpg) and no odd, rich exhaust odors either.
The original lasted 170K miles and went through 3 O2 sensors until it finally was depleted enough I needed to change it.

Just want to make sure before I dump 300 dollars into a new converter...