Field answer
Direct answer
A low-air warning means the brake system may not have safe operating pressure and the vehicle should not be driven until the system is checked and corrected. Use the current state CDL manual, company policy, and a qualified mechanic for live vehicle defects.
How to use this answer
Read the answer once, then prove it by choosing an answer in a practice question before looking at the explanation. If the miss repeats, tag the domain as CDL air brakes and drill a smaller set before returning to mixed practice.