Air horns on Pierce Saber

[Juice]

Has anyone else had problems with the air horns of a Pierce Saber, particularly the newer ones? We have a 2011, and about 2 months ago, they started off intermittent when we'd try using them, and then quit working all together a few weeks ago. Fast forward to this week, we were able to knock open a valve running up under the cab, and they began working again. To know how to approach it, should it ever happen again, is it really the valve, or is there a bigger problem?

 

Thanks,

Trav!