Air leak under the dash

The valve may be cracked (behind the dash). On our old 2003 truck, we had to have this replaced once. If it leaking very loud, I would have a dealer check it out. The part is only plastic and easily can wear out. Hope this helps.

 

if you have a leak in a brake chamber or a air line, it is common to hear it behind the park brake in the dash. check outside the truck for leak source again. it could also be the dash valve too.

 

check air swith manyfold. hidden with trash. check quick connect fittings.

 

Yea this is normal that the pop out valves on the dash wear out and need replaced. Had the same issue with the international 9300 I drove last year. They would leak hissing air and it got annoying but they finally gave up to where they wouldn't even stay in on their own when pushed in anymore. But while replacing the pop out valves you might wanna go ahead and test the lines back there while the dash is apart and make sure there aren't any other leaks. in the connecting lines as well. May save you some trouble later on if one happens to be dry rotted. The valve set aren't expensive and easy to do on your own which could save you some bucks on labor. I'd say find a used valve set of pull one from a wrecked truck, teflon the fittings, hook the lines back up test for pressure and leaks after its mounted back in place under the dash face. If you only hear it inside then its in the dash or on the firewall inside under the dash somewhere but replacing the pop out valve set is pretty simple and straight forward.

 

Where is the air switch located

 

Under cup holders is air pressure switches. But remove the bottom plastic also.