Practice question Low-air-pressure warning (buzzer/light) must activate no later than: 20 psi60 psi100 psi120 psi Answer: B — 60 psi The correct answer is shown above. Try the full quiz for additional practice. Practice more: USPS MVO Exam Practice Questions - USPS Exam 220 230 240 - Motor Vehicle Operator Tractor Trailer Operator (Driving Experience Assessment) Exam →