Question A low air pressure warning signal: Answers Is not recommended on vehicles with air brakes. Is required on vehicles with air brakes. Is optional on vehicles with air brakes. Explanation Any vehicle with air brakes must be equipped with a low air pressure warning signal. Take a FREE Practice Test Now This questions appears in the following tests: Connecticut Knowledge Test Class A , Vermont Double , Arizona Air Brakes , Arkansas Air Brakes , Maryland Air Brakes , Missouri Air Brakes , Nevada Air Brakes ,