Hello again, The SD40's horn has broken for me multiple times on Fremont Ascent. I ring it at crossings and after 4 rings (usually in shorter succession) it stops working and the horn sound is replaced by a loud sound of a button being pressed. If I save and reload the bug is gone until I go to ring the horn in short succession again. Also note by short succession I don't mean like a child mashing a horn haha, but more ringing it a few times over a 5-6 second window.
Since I purchased the CSX C40 addon a couple of days ago, the horn is doing as you say. I don't mash it either. I use it as per US regs approaching a crossing along with the bell until over the crossing. You are lucky to get a few goes before it stops working. Deffo a bug, and one that needs sorted for US routes as its integral to accurate operations. So it also affects Sand Patch Grade.
strange... my horns actually don't cut out anymore. ever. I don't know what I have done but it's fixed for me.