2 ways to get the error codes
the display will show an abbreviation of the error code but for the height encoder there are many variations of that and it is generally accompanied by an error number. When you access the main controller (1310) the first numbers displayed are the errors stored in the controller and you can scroll through them using the control handle. It will show the abbreviation first, then followed by the error number and then hours.

the 2nd way to get the codes is with a curtis handset connected directly to the controller/manager.

now from my experience and what has already been suggested the height encoder has always had issues with the wiring harness at the encoder , yale even had an updated part with a new harness and connector issued not long after this system was implemented on to this truck.

I would concentrate on that area first. Also make sure the battery is in good condition and fully charged as well. These trucks are very voltage sensitive and a defective battery or dead battery can trigger false codes.
If you don't have a manual on this truck you should get one, you will need it.