CDL Air Brakes Practice Test

If your vehicle has air brakes, you must pass the Air Brakes test to remove the restriction from your CDL. This section is famous for its exact numbers — and that's where most people lose points. Our 89 practice questions drill those numbers and explain the reasoning behind every answer.

What's on the Air Brakes test

Covers the parts of an air-brake system, dual air systems, the supply and service lines, the low-air warning, spring (parking) brakes, the air-brake inspection and leak-down tests, brake fade and safe braking on downgrades, and antilock brakes (ABS).

Study tips to pass

• The low-air warning must come on before pressure drops below 60 psi.
• Spring brakes apply automatically at 20–45 psi; the governor cuts out around 125 psi.
• A dual system should build from 85 to 100 psi within 45 seconds; don't drive below about 100 psi.
• Drain the tanks daily, and never "fan" (pump) the brakes on a long downgrade — you'll run out of air.

How it works

Each question on CDL Prep Hub comes with a plain-English explanation, so you learn the "why" behind every answer. Aim for 80% or better — that's the passing mark in most states — then take the timed exam simulator to rehearse the real format. No account needed; your best scores save in your browser.

Other CDL practice tests

Study material based on the official CDL manual. Not the official state exam — always review your state's CDL handbook before testing.