During the air brake check, what should you do to test that the trailer's brakes actually apply when the trailer supply valve is closed?

Pick an answer

1. Rely on the dashboard warning light alone with no physical check
2. There is no way to test this before driving
3. Close the valve and confirm the trailer brakes set, often by trying to pull against them gently
4. Only check that the trailer's air lines are still connected properly, though that's not how closed actually works

Correct!

Not quite. The correct answer is highlighted.