How can you check that the spring brakes come on automatically?
Answer: Continue to fan off the air pressure by stepping on and off the brake pedal to reduce tank pressure. The tractor protection valve and parking brake valve should close (pop out) on a tractor-trailer combination and single vehicle types when the air pressure falls to the manufacturer's specification (20-40 psi). This will cause the spring brakes to come on.
If the answers is incorrect or not given, you can answer the above question in the comment box. If the answers is incorrect or not given, you can answer the above question in the comment box.