If the low pressure warning signal is not working, what may occur in a single circuit air system?

• A. Brakes lock up
• B. No brakes at all
• C. Sudden emergency braking
• D. Engine stalls

Answer: (C)

Air brake systems rely on compressed air to operate the brakes, and a low pressure warning is there to alert you before pressure gets low enough to trigger automatic braking. In a single circuit system, if that warning isn’t working, there’s no early notice as pressure drops. When the pressure falls to the point where the system automatically engages the emergency brakes, you get a sudden, hard brake application. That abrupt stop is a protective feature to prevent loss of braking power, which is why sudden emergency braking is the best answer. Other outcomes like no brakes at all or the engine stalling aren’t the typical result of a failed warning signal in this setup, and brakes locking up would come from a different failure or driving action, not the absence of the warning.