Surprise when checking cats and sensors!

I have this 2002 pathfinder we bought about a 1.5 years ago. It came cheap due to going into limp mode. I cleared the codes when i got it home and limp mode stayed away for a while.  then it came back more frequently until i couldn't get it to stay out of limp mode so it has been sitting. I decided to attack a few issues. Its currently got the intake manifold off so i can get the knock sensor, coolant hose, valve cover seals and check the intake system out for issues. 
 

I decided hey, lets be crazy and pull these cats off to see if they are indeed bad and causing the codes and issues.  
 

passenger side off first, cat looks decent i guess? 

the o2 sensor looks "lean" and white

the pre-cat sensor has seen better days. 

both pre cat o2 sensors have no covers. Im thinking this was a trick to get the first o2 sensors to read better than the after cat o2's. 
 

here is the big surprise. I was expecting and kinda hoping that i would find the cats messed up or clogged. Passenger side was good looking, so i didnt expect to find the driver side like this. 

gone. Friggin done run-offt. 

I was going to re-do the exhaust anyway, from the cats back. Guess i'll be doing the whole thing and ordering some aftermarket cats. And all new oxygen sensors. Off to RockAuto. 

Exit, stage left even.

Did it end up in muffler/resonator?

Im not a exhaust expert, although i do produce a lot of exhaust. Is it possible for the brick to have left that clean? Does it take some outside effort to get it totally out?  Im thinking this pathfinder got sent through some buy here/pay here shady lots that may have done some shenanigans. Its had a pretty crappy repair to the rear corner too, at least 1 really crappy paint job. 

Looks like the cat matrix on the other side is no longer attached where it should be....

Thermal stress can break the cores up fairly easily. Everything looks like it got real hot. See how what's left of the right side core is sagging and melted in spots? Possible causes: bad O2 sensors, flooding injector, massive vacuum leak under prolonged high load, extreme pre-ignition. ECU might have compensated for a percieved lean condition and over-fueled to the point of cat meltdown and subsequent disintegration. Driving a wounded steed hard when it's clearly suffering (previous owner, out of frustration) might do all of the above.

Or yeah, some hack was there first and just broke some E36 M3.

I had an '04 Mini Cooper S.  Lots of mods that made it an absolute blast to drive.  It was a 4 passenger go cart.  It had a stock cat connected to a stainless header upstream and cat-back exhaust downstream.  Began to notice a difference in sound and power during change from accelerate to decelerate (more than just change in throttle position would create) as well as a growing rattle from the exhaust in the cat area.  After a  month or so I dropped the exhaust and was amazed at what I found.  No pic unfortunately, but the cat core was completely loose.  It had rounded off all of the edges so that it was a sphere and literally looked like a softball.  Hold it nose down, the core rolled forward.  Nose up, the core rolled to the rear completely blocking the outlet!  

I figured that 4 cyl vibration had to have been a culprit as the header eliminated two flex pipes that had been on the original 4-2-1 downpipes.  The resulting vibes had to have broken the core free.  I replaced the cat with an aftermarket hi-flow one now properly isolated by a flex pipe.    

Lesson learned!