@camng, Did you take off the front passenger wheel and the associated wheel well plastic? You may need to get to it from the side instead of from the top or bottom.

 

I'm struggling with this right now actually on my 2010x. That little SOB is frozen in there pretty good. I can get to it with a 20" long 3/4" extension coupled with an angle joint to either a crowfoot or socket O2 adapter, but it doesn't seem to matter. Even hitting this with an impact or breaker bar doesn't seem to be working. Even heating up the manifold first does nothing. I'm thinking i may need to drop the manifold to get a direct impact on the bugger.

 

Soak them really well with PB-Blaster. I changed both on my 2001 a few years ago. They were the original factory units. Really well means overnight, and repeat over several days...

 

I've been using Kroil for a few nights now and will keep trying. The long extensions tend to blunt the effectiveness of an impact. I almost need a double box end type wrench to get an upward facing impact gun on it

 

Finally got it. Trick was to pull the passnger wheel, remove the one clip on the splash shield in the wheel well, and get at the thing with a (crowfoot O2 sensor socket)-(impact swivel joint)-(6in impact extension). Got the impact more directly on it. Oh yea, and I also made use of my new Dewalt DCF961 which was probably overkill for this, but is a freaking beast.