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

Hello, I had an inspection, and they notice the brake valve , yellow knob is doesn’t pop out when 40-20 psi. It doesn’t pop out not even when it’s 10psi.
I have an Freightliner Columbia glider. Can anyone help me with some info, much appreciated, and thanks in advance.

 

So I’ve read about the tractor protection valve, and then I’ve read about the sensors, electric air sensors that are inside dash. They’re bunch of them, and very truck is different, and when you go to dealer they can’t say what you need unless you remove the sensor

 

Tractor protection valve, where is located? Thx. I’ve replaced couple of dash valve, myself, before. The tractor protection valve is $70, the red&yellow knob valve is $260

 

The red one is popping out, but the yellow doesn’t. It’s a rebuilt kit, with o ring silicone gaskets and grease, but freightliner like to sell the valve, instead of the rebuilt kit that cost no more than $20-$30. I don’t believe cleaning it, will do any good. I’ve rebuilt it 2 times, but it’s a pain to remember or to find the exact part number for that kit, and if you don’t ask for it, they don’t wanna look for it, for the part number anymore. You have the know the part number to get it.