Your furnace has an exhaust fan. It's the first thing you hear when the furnace comes on. The pressure switch insures that the exhaust fan is running. That code could mean that the exhaust pipe is blocked or the intake pipe could be blocked. Some condensation could of gotten into the the switch itself. The switch itself could of course be bad. Or there could be a problem with the exhaust blower. Or even some other problems.
At any rate, your switch is opening up during operation or maybe not even closing and preventing the furnace to cycle. There are several things to check. That part should be under warranty at less than a year old. I would recommend you call your installer.