Built By A Driver
Air Brake Test Steps for CDL Drivers
Free: our one-page checklist
Built from 20 years over the road. Print it and keep it in the door pocket.
Truckers Resource Hub Pre-Trip Checklist (PDF)
One page with check boxes. Walk the truck with it before every trip so nothing gets missed.
Send me the checklistIf you drive anything with air brakes, this test is part of your life. It is on the CDL skills test, and it belongs in your in-cab pre-trip. This is the whole check in order, the way it runs in the cab.
Before you start
Park on level ground. Chock the wheels before you release the parking brake, so the vehicle cannot roll. You need the engine, the gauges, and about five minutes.
Do the steps in order. If one fails, stop there and get it fixed before you move on.
The nine checks
Engine on or off matters, so it is tagged on every step.
Build air to governor cut-out
Start the engine and let the air system build until the governor cuts out. Watch the needles climb. Do not rush this part.
Governor cut-out: about 125 psi (manufacturer range 120 to 140)
Checks: a full charge before any of the tests.
Static leak test
Shut the engine off and release the parking brake by pushing in the red and yellow valves. Let the gauge settle, then time one minute and watch the air gauge.
Limit: under 2 psi lost in one minute (single vehicle), under 3 psi (combination)
Checks: catching a leak anywhere in the system while the brakes are released.
Applied leak test
Fully apply the foot brake and hold it steady. After the first drop, hold for one full minute and watch the gauge.
Limit: no more than 3 psi lost in one minute (single vehicle), 4 psi (combination)
Checks: leaks in the brake chambers and lines while the brakes are applied.
Low air pressure warning
Leave the key on so the gauges and warnings work. Fan the brake pedal, stepping on and off, to bring the pressure down slowly. Note the pressure when the warning light and buzzer come on.
Warning must come on before pressure drops below 60 psi
Checks: proving the warning works before you need it. In a dual air system, check the tank with the lowest pressure.
Spring brakes pop out
Keep fanning the pedal down slowly. The parking brake valve pops out, and on a combination the tractor protection valve too, and the spring brakes apply. Stop fanning once they pop.
Pop-out: 20 to 45 psi, per the manufacturer's specification
Checks: confirming the spring brakes apply on their own when air runs low.
Pressure buildup test
Restart the engine and run it at operating RPM. Time how fast the pressure builds.
Dual air system: 85 to 100 psi within 45 seconds
Checks: a weak compressor or a restriction in the system.
Governor cut-in and cut-out
Let the pressure build and drop a few times. You should hear the compressor stop pumping at the top and start again at the bottom.
Starts pumping at about 100 psi, stops at about 125 psi (confirm against the manufacturer's spec)
Checks: that the governor controls the system pressure the way it should.
Parking brake test
With the system charged and the chocks removed, set the parking brake. In a low gear, gently pull forward against it.
The vehicle must not move
Checks: proving the parking brake holds.
Service brake test
Release the parking brake, move forward at about 5 mph, and apply the service brake firmly. Feel for pulling to one side, an unusual feel, or a delay in stopping.
No pull, no odd feel, no delay
Checks: the brakes working together under load.
Mistakes that fail people
- Key fully off during the tests. The gauges and warnings do not work, so you and the examiner see nothing.
- Not holding the full minute on the leak tests. Sixty seconds, steady foot, eyes on the gauge.
- Fanning too fast. Fast fanning drops the pressure too quickly to tell when the warning comes on or the valve pops out. Fan slowly and on purpose.
- Releasing the parking brake before chocking the wheels. The vehicle can roll.
- Moving on after a failed step. If the warning does not come on or a valve does not pop, stop. A truck that failed an air brake check stays parked until it is fixed.
Do this on every in-cab pre-trip
The walkaround finds the visible problems. This test checks the air system itself. Brake systems were the top vehicle out-of-service violation at the 2026 CVSA International Roadcheck, at 3,379. Together with defective brakes, brake-related violations came to 5,451, or 39.1% of the total. See the CVSA results.
Want the full walkaround to go with it? The Pre-Trip Inspection Resources page has the complete routine.
Studying for your CDL?
The Real Trucker's CDL Study Guide
Written by a 20-year owner-operator, not a test-prep company. It cuts through the confusion so you can pass your test the first time.
Get the Study Guide →Air brake test questions
At what psi should the low air pressure warning come on?
Before pressure drops below 60 psi in the air tank. In a dual air system, check the tank with the lowest pressure.
How much air loss is allowed in the leak test?
In the static test, with the parking brake released and the foot brake not applied, the loss should be under 2 psi in one minute for a single vehicle and under 3 psi for a combination. In the applied test, with the foot brake fully applied, no more than 3 psi in one minute for a single vehicle and 4 psi for a combination.
At what pressure should the parking brake valves pop out?
Between 20 and 45 psi, per the manufacturer's specification. That is when the spring brakes apply.
How fast should air pressure build in the buildup test?
In a dual air system, pressure should rise from 85 to 100 psi within 45 seconds with the engine at operating RPM.
Should I do the air brake test every day or only for the CDL test?
Treat it as part of every in-cab pre-trip, not just a test-day exercise. Your carrier's policy and your state's rules set the exact requirement.
Does the order of the air brake test steps matter?
Yes. Each check builds on the one before it, so do them in order and stop if one fails. Some states and schools start with the low air warning test, so follow the order in your state's CDL manual.
General reference only. The figures follow the model CDL manual as published in state CDL manuals, and they can differ slightly by state, vehicle, and manufacturer. Follow your state's current CDL manual, your carrier's policy, and the current regulations.
Checked against: Georgia CDL manual, air brakes section and Kaplan CDL air brake quick reference.