When testing the air brakes on a triples combination, what should happen at each trailer as the system builds pressure?

Pick an answer

1. Only the first trailer needs to show a pressure increase
2. Trailers should never show any change in air pressure during the check, since the system is sealed off from each unit
3. Each trailer's air tanks should charge and its brakes should apply and release correctly, in sequence with the others
4. Pressure should only build in the tractor's own tanks

Correct!

Not quite. The correct answer is highlighted.