Valve under fifth wheel is leaking air

Thank you for sharing

 

Sounds like a air chamber on the trailer is leaking and backfeeding through the valve.

 

The valve under fifth wheel, is that the ABS valve?

 

If air isn't leaking with only the yellow button in, @kwswan said, probably a trailer brake chamber.

With red button in, pull your blue air line and see if air is coming out of the trailer gladhand

 

No luck where? You're gonna have to explain

 

If you can't point, we can't help.

Sometimes, in trucking, you have to take off the flip flops.

 

I had to change mine once. Only the valve portion, not the part with abs wires running to it. It wasn’t expensive. That’s all I remember.