Just had a bout of trouble with my furnace and found rare condition. The error code for ID fan pressure switch failed closed can also be caused by poor connection on the 5 pin ID fan/Igniter connector.
Board failed and I replaced and got the 3 red flash error code for switch failed closed, checked it out and it was obvious that the switch and wiring were OK.
Spent the next couple days thinking and tinkering with the furnace, even call an "expert" and was told the board bad ( I bought the board from him). Before removing and sending it back, I went thought and checked all my connection a third or fourth time and noticed that when I push on one of the wires in the five pin connector it moved. Made sure all were seated and furnace started.
A loss of external connection or open circuit can cause a false error code. Just thought I would put this out there.
Board failed and I replaced and got the 3 red flash error code for switch failed closed, checked it out and it was obvious that the switch and wiring were OK.
Spent the next couple days thinking and tinkering with the furnace, even call an "expert" and was told the board bad ( I bought the board from him). Before removing and sending it back, I went thought and checked all my connection a third or fourth time and noticed that when I push on one of the wires in the five pin connector it moved. Made sure all were seated and furnace started.
A loss of external connection or open circuit can cause a false error code. Just thought I would put this out there.

