oh and i liquid wrenched the **** out of it like every 20min for 2 hrs, but didn't work.. the torch did the trick tho

 

i had the same problem on an almost brand new IX. I tried pb blaster but didn't work, so ended up getting a torch and put the flame near the base till it got real hot, then quickly broke it loose with a long 1/2" breaker bar

 

This is a pretty common problem because, as I have read from a couple of sources, Mitsu has a habit of cross-threading that rear O2 sensor from the factory; at least that's the way mine was when I tried to take the exhaust off after about 3,500 miles. I broke mine loose very easily, but then it got stuck after about 1 full revolution. I worked at it with a leverage bar, but couldn't get it to move.

I just went to the local auto parts store, and got the cheapest 4-wire O2 sensor (got one for $40, actual application was some Chrysler vehicle). I wired that into the car, adding the spark plug defoulers to prevent the CEL, and went on my way. The original O2 sensor is still in the catalytic converter sitting in my garage.

 

I jacked the car up, put the wrench on the sensor and placed another jack under the wrench. started to jack the wrench and i was able to get the sensor loose.

 

Removing the sensor is the first thing you should have done. If the sensor is stuck all you have to do is start the car & let it warm up......the sensor will come right out every time.

 

AWSOME!

 

when in doubt.. remember the old adage... righty tighty lefty loosey?

on my old DSM when the O2 got stuck I used an air chisel... took it right out after about 2 min.