Hello! Need help please. The yellow knob is not popping out.

This morning I had to move one of the new WS that was delivered last night. I hooked the trailer air lines to it, ran it up to full pressure, pushed in both valves, shut it down, drain the air and guess what?

The red one popped, the yellow one didn't.

This truck has 634 miles on the clock.

 

Does the red knob (trailer parking break) pop out?

 

Buy the entire dash valve. You said you rebuilt it twice, it's time for a new one.

 

The tractor protection valve is nothing more than a valve that when air is applied from the red button, it opens the valve and allows service air to the trailer. If you disconnect the red line from the trailer while the red button is pushed in, the red button should pop out, but I’ve never been in a truck where the yellow button will also pop out. In the most basic terms, yellow is to set the tractor brakes, and red is for trailer air supply (which when pulled out also applies the trailer brakes).
Also, you have systems that have a red and yellow button, but there are some that also has a blue button.

 

So you've never driven a truck that's never had a properly functioning valve.

Even the 88 kw I drove popped both valves.

 

They both will pop out if you have a loss of air in the whole system, but if you just have a loss on the trailer supply (as can be simulated by disconnecting the red trailer line while the red button is in) only the red button will pop out. It’s been that way on every truck I’ve driven, but the newest truck I have is a 1998.