I think you mean you can fix his problem which is more how one fixes a bad appendix(assuming your surgeon uses flame throwers), not actually fixing his Gem car.
Well then I can assume this was not going to be the swinging keys theory. This does not need to be a complex switch, but all connections should be inspected.
You seem to have isolated an issue with the park brake with a random -04 code. Fix that first.
Being a new owner to a Gen1 Gem car you may not be aware there was a DC Converter upgrade/wiring update involved with your car. Depending on the status of the update on your car, it might be the next item to look at.
If you have not discovered the archives yet, Use the search tool(magnifying glass) found in the upper right of this page and enter a few key words (such as Wiring Update). Here are two good examples of past conversations.