At what psi should the low air pressure warning come on before the tanks fall below a certain pressure?

• A. 40 psi
• B. 60 psi
• C. 80 psi
• D. 100 psi

Answer: (B)

Low air pressure warning is there to alert you before the system gets too low to safely operate the brakes. In most Class A air-brake setups, that warning is set to come on when tank pressure falls to about 60 psi. This gives you enough time to slow down and stop safely before the air supply is too low to apply the brakes effectively. If the warning came on higher than that, you’d be warned too early and could ignore it; if it came on much lower (like 40 psi), you might not have enough time to react. So 60 psi is the standard, practical threshold.