Generally what happens is the contacts burn out at the position where you cruise on the highway. 55-66MPH or around the 2k range. This can vary of course, but this is where I've typically seen it fail. The best way to test it would be with an oscilloscope, but most of us don't have one of these in our home shops but you can visually see where it failed.
I would say if you can break into it, you might be able to clean these contacts up or repair them, but it's hard to say. I think most people just replace them. Good luck!
