Been fighting with this car for over a year since I was hit by another driver. Dealership can't figure it out. Yesterday while tinkering with it I slammed my fist down on top of the instrument panel out of frustration and everything cleared like it was brand new. Went on a test drive, gauge readings died and all the faults/errors came back, so I hit the dash again, and they cleared. When I get the dash off this weekend, is there anything specific I should be looking for?

 

A loose connection in the wiring! Start by looking behind the covers on each end of the dash (instrument panel). They merely pull off but you do need to pull part of the door seal away first.
There are a couple of multi-connectors here. Try uncoupling and re-connecting them.
Second stop would be the distribution board / fuse panel in the passenger foot-well. (It's in the driver's-side foot-well in right-hand-drive cars so I'm assuming they wouldn't move it). Check the various connectors going in and out of this.
If the problem is still there then the instrument panel will almost certainly need to come out as it seems the problem lies there judging by your description of the temporary "cure".

 

I pulled the instrument panel and there are only two connections back there which I unplugged and reset. No change. Replace instrument panel?

 

I pulled the instrument panel and there are only two connections back there which I unplugged and reset. No change. Replace instrument panel?