What does the tractor protection valve do if the trailer's air supply line breaks or separates?

Pick an answer

1. It shuts off the engine to force the vehicle to stop immediately
2. It has no function related to a broken air line, only to trailer lighting
3. It opens fully so the tractor sends every bit of its remaining air to the trailer regardless of the leak
4. It closes automatically to keep the tractor's own air supply from draining away through the broken line

Correct!

Not quite. The correct answer is highlighted.