Seven-Step Pre-Trip Air Brake Test
The mandatory pre-trip sequence that proves your brakes will work when you need them.
Endorsement: Air Brakes · Source: FMCSA CDL Manual (public domain)
The seven-step pre-trip air brake test is the single most important pre-trip procedure for any vehicle with air brakes, and CDL examiners watch for it religiously. Step one: with the parking brake set, transmission in neutral, engine off, and air system fully charged (governor cut-out, around 125 psi), check that the air compressor governor cuts in and out by pumping the brake pedal to lower pressure and letting it rebuild. Step two: check that pressure rises from 85 to 100 psi within 45 seconds for combinations and within 30 seconds for trucks and buses with the engine at operating rpm.
Step three: shut the engine off and check the air-pressure leak rate by holding the brake pedal applied. With the engine off and brakes released, the system should not lose more than 2 psi per minute on a single vehicle or 3 psi per minute on a combination; with the brakes applied, the limit is 3 psi single, 4 psi combination. Step four: pump the brake pedal to lower air pressure and verify that the low-pressure warning device activates before pressure drops below 60 psi.
Step five: continue pumping; the parking brake (spring brake) must apply automatically before pressure drops below 20 psi (typically 20-45 psi range depending on vehicle). Step six: rebuild pressure by starting the engine and letting the system reach normal operating range, then test the parking brake by releasing it, putting the vehicle in low gear, and gently trying to pull against the parking brake to confirm it holds. Step seven: at idle, with parking brakes released, roll forward at about 5 mph and apply the foot brake firmly. The vehicle should stop straight without pulling. Any deviation from these steps or any failure to meet a numerical threshold is an automatic skills-test failure.
Key terms to memorize
- compressor
- governor
- supply tank
- service tank
- brake chamber
- slack adjuster
- low-pressure warning
- spring brake
- application gauge
Other Air Brakes topics
- Air Brake System Components — How an air brake system actually moves a brake shoe — every part, in order.
- Dual Air Systems — Why modern trucks have two independent air brake systems and how they protect you.
- Low-Pressure Warning Devices — How the system tells you that braking authority is about to be gone — and what to do.
- Parking Brake System — Spring brakes, holding power, and why you never use parking brakes as service brakes.
Test what you learned
Now that you have the Seven-Step Pre-Trip Air Brake Test material in your head, drill the Air Brakes practice test. The questions are drawn from the same FMCSA source material this article paraphrases. For state-specific framing, jump to your state page and pick the Air Brakes test for your jurisdiction.