2014 T680 Air exhausting at firewall

2014 t680. There are two squares beside foot valve on firewall. One has airlines connected to push pull fittins. Other square is empty ports with no lines. One of the empty ports on this one leaks air only when trailer valve is pulled out. Does this mean the dash valve is bad? Thanks in advance and happy trucking

 

Yes thats correct. How would I check that?

 

Yep. Removed red glad hand and its exhausting out of trailer connection now and not at firewall. Sounds like you were right. So what valve exactly is it i need , sir?

 

Wonder if that may also explain why when truck gets 25 psi application air, trailer is only been getting maybe 10 psi so trailer not stopping as much as truck

 

Alright, thanks so much. Was bout to go buy the dash valve from dealer as they said that's probably the problem. You saved me money and time. This forum has helped me tremendously several times because of people like you that take their time to help another. Have a great day my friend.