Which vehicle must have low air pressure warning signals?

• A. All of them
• B. Only trucks
• C. Only buses
• D. Only tractors

Answer: (A)

Low air pressure warning signals protect you by alerting the driver as soon as the air brake system pressure drops to a dangerous level. Any vehicle that uses an air brake system must have this warning, so you’re alerted before the brakes could fade or fail. The warning is typically a light or audible alert that activates when pressure reaches about 55 psi, giving the driver time to take action. Since trucks, buses, and tractors commonly rely on air brakes, the requirement applies to all of these types, not just one. Vehicles without air brakes don’t need this signal because there’s no air-pressure system to monitor.