Trane High E has code 2

I have a Trane High E packaged gas heat and AC unit outside. When ever the weather is damp or rains the furnace try's to start but shuts down and sets a

code 2.

I have replaced the igniter and still does it.

Service people blame the air filter but I have replaced it many times when they come out they reset the computer and it starts but they never have fixed the problem. This has been going on for 4 years.

Trane High E has code 2