So not only do I have a rattle near my catalytic converter, I'm getting the infamous P0420 code. I recently moved into a house that is in a city that does not perform vehicle inspections. So would it be worthwhile to go ahead and replace the mid pipe to a cat-less version and get a tuner (to turn off the code) rather than replace the bad O2 sensor? I haven't talked to a dealer / repair shop yet, but my brother-in-law recently got quoted for the same 02 fix and it was north of $450.

Any opinions?

 

O2 sensor is real easy to replace yourself...the rattle could be your heat shield coming loose on your Cat.

 

It means you've got a bad catalytic converter. I didn't want to spend money on my 10 year old truck on a new converter, so I tried this $5 solution and it worked! Took more time going and buying the defoulers than the work to get it installed. Oh yeah, rent the o2 sensor removal tool when you're buying the defoulers. It's the downstream O2 sensor by the converter. Several thousand miles and still no check engine light: