Question If the emergency air line loses pressure: Answers The Anti-Lock Braking System will activate. The service air line will activate. The emergency brakes will activate. Explanation The emergency air line controls the emergency brakes on a combination vehicle. A loss of air pressure in the emergency line will cause the emergency trailer brakes to activate. Take a FREE Practice Test Now This questions appears in the following tests: Iowa Double , Virginia Tank , Arizona Combination , California Combination , New Mexico Combination , Rhode Island Combination , Vermont Combination , Washington Combination ,