Final answer:
Once a trailer is fully coupled to the tractor and the air system is charged, the tractor protection valve becomes operational, ensuring safety by preventing air loss from the tractor.
Step-by-step explanation:
After a trailer has been completely coupled to the tractor and the air supply is charged, the tractor protection control valve will be operational. This valve is a safety device that prevents air from escaping the tractor if the air pressure drops too low, ensuring the tractor's brakes will engage automatically to prevent a trailer separation.
The valve doesn't turn green as it is not a visual indicator, but rather it becomes active to protect the air supply and maintain brake functionality. The proper coupling of the trailer ensures that the air lines are connected and the valve can function as intended.Once a trailer is fully coupled to the tractor and the air system is charged, the tractor protection valve becomes operational, ensuring safety by preventing air loss from the tractor.