The brake-system warning light or buzzer is designed to alert you when:
Correct. The brake-system warning device alerts you to dangerous low air pressure — typically activating at or before 60 psi.
CDL Practice Question #161
Category: Air Brakes
Why this question matters
This question is one of 71 in our Air Brakes bank. The reasoning above comes directly from the AAMVA CDL Manual, the source document used by every U.S. state DMV. Memorizing the underlying rule — not just the letter answer — is what separates passing on the first attempt from a return trip and another fee.