Red knob not popping out.

My advice is to use the books and info that will be used during an inspection, not any third party books including the manufacturers. You are not trying to do in-depth troubleshooting, just making certain the system is working per the Regs you are required to follow.

The CVSA North American Standard Out Of Service Criteria which states:

Tractor Protection System
Inoperable or missing tractor protection system components including a tractor protection valve and/or trailer supply valve. (393.43(b))
NOTE: An inoperative tractor protection system is defined as one of the following conditions:
1. The trailer supply valve fails to close before pressure drops below 20 psi (138 kPa) in either the primary or secondary system.
2. When air escapes from either glad hand when brakes are applied after the tractor protection valve has closed.

For testing, the inspector will follow the procedure in CVSA bulletin 2010-01. Note it’s not instantly but before it drops below 20 psi.
http://cvsa.org/wp-content/uploads/2010-01-Tractor-Protection-Systems-Revised-05-19-10.pdf

 

Well then i think you are overthinking this valve thing. Get or put a new one on. After a few months of use it will probably do exactly what its doing now. I have been Dot,d , Puco'd in 43 yrs and never red tagged for this valve issue. They have checked it two ways. #1 they had me pump my foot brake till air psi went down to 60 or lower to see if knob popped.#2 he had me set the tractor brakes. Flipped off service gladhand, then he hustled up to cab to watch air guage drop. #2 method is a better check in my opinion, as thats a sudden loss of air.In the #1 you are wearing your footvalve out to accomplish next to nothing.

 

Not overthinking anything, just stating what’s required and how it’s achieved. The two methods you mentioned are not compatable with procedures the CVSA established and neither test the T/P valve. Just because the red button pops doesn’t mean the T/P valve closed.

 

if its a freightliner cascadia up under the dash above the gas pedal there are air switches it will be above the others with 2 wires going to it there should be a tag on the wires you are looking for the wires that say parking brake remove replace that switch

 

How do you do a leak down test in an automated trans. I mean you can't put it gear with the engine off and pump the pedal till the knobs pop out right?