It turned out it was a board in the grain tank, not the corner post. I don't know what they call the boards, but it wasn't the mother board.
There are a lot of functions that won't work with an error code with a priority code of 1. So if the only display you get on your cornerpost is an error code, you have to fix that immediately.
As far as the service manager guessing, that is straight from detac(?). The computer said to swap boards with another machine, if available. If the problem goes away, replace the board. Another machine wasn't available, so I took the gamble with a new board.