If it's throwing a code then that is where you need to start , diagnostics are the name of the game.
I have a theory however OP
There are two possible causes I can think of
First would be the 'lower' portion of the switch has failed, if this is the case driving it to above 35mph for a minute will make it lower itself.The even more common issue with it would be that the exhaust muffler on the compressor has clogged This can be removed to lower it temporarily (it'll be quite loud) and then replace the muffler and the dryer as soon as you can. The muffler is a brass cone that sits on the front of the compressor. Remove the spare wheel and clam shell cover, then remove the muffler. When it clogs, it is a sign that the dryer is separating.