yeah this must be a fairly new truck and this 1232E series curtis controller i was assuming it was pretty much the same as the standard 1232 controller. Thats where i got my information from off of fsip's website. (flight systems). I'm taking a guess that it is probably very similar but probably has new features in it compared to the old model controller.
I would suggest that if this truck is in warranty to call yale and have them look at it.

Now as far as accessing the yale diagnostic if it is the same as the older units you just have to hold the horn trigger button and turn on the key and then release and pull the horn trigger button a couple of times real quick (within a couple seconds if i remember right), to get into the system. It will then make you go through a calibration routine with the control handle and then once complete you can navigate the menu system and find error codes and change settings, enable and disable functions etc.
Note: you will need the yale service literature for this though to get the correct parameters for it.

You can also use the latest version curtis handset or pc programmer software with special cable and do some programming in the controller itself but that is just motor controls, it is not truck model specific setup controls.
If by chance you cannot get it to allow you in then there may well be an issue with the controller and it might just have to be replaced.