Somehow, while tsking out my diff, one of the captive nuts that hold the "H" bar in place spun. The bolt is cross threaded it seems and its halfway out. I can't get it out. What recourse do I have?

 

You can typically get the right size of channel locks above the PPF to hold it in place. If that doesn’t work, unbolt it at the trans and drop the entire diff/ppf as one, then cut the offending nut off from the top.

 

I probably didn't describe it correctly. My car is a 2001 se. It came with a big h shaped reinforcement bar. The bolt I'm having issue with is towards the front of the car. The nut is enclosed in the frame. There's no way to get a wrench on it. I'll get a picture of it later.

 

You mean the subframe brace like the one below? IIRC 4 bolts go into the subframe and 2 go into the chassis, which I assume are what you're referring to.

 

Had the same thing happen to me. Only solutions are to cut off the bolt - and leave the damned thing to rattle around in the bottom of the car - or, cut a hole somewhere and fish it out.

 

No need to cut a hole. In the driver and passenger footwells there are square covers glued on that when off. (Dry Ice) allow you to use a borescope or magnet on a wire to fish things out of unibody areas.

If you look at the square cover, it accesses the frame and area above the bolt in question. The braided line runs through the same unibody area and is just above where the bolt passes into the unibody.
That little plug just inbd from the braided line is directly above one of the bolts.

 

That should work for a bolt/nut in the front, but the one I broke off is behind the driver seat. I'll have to check if there are similar access holes in the rear section.

Poscat for good suggestion.

 

That's the brace I'm talking about. The loose nut and bolt rattle now. Sounds like a bell when I start the car. I'll cut it off and see about fishing it out.

 

There are also square frame access plates under the seats.