How to Check Truck Air Brakes

by Steven W. EasleyUpdated July 21, 2017
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The air brakes on a truck are a vital system which must be inspected and maintained in order for the truck to be operated safely. The air system operates within a normal range of 120 to 150 psi and is capable of stopping a heavy vehicle weighing in excess of 80,000 lbs. The proper inspection and maintenance of this system is essential to the safe operation of a combination vehicle. A minor air leak can prevent the system from operating properly and can cause brake failure.

Complete a walk around inspection of the truck. A pre-trip and post trip inspection of your vehicle should be conducted each day. Some states do not require that a pre-trip inspection be logged, but a post trip inspection is mandatory and much be entered into the driver’s daily log.

Chock the truck tires. Crank the truck and allow the air pressure to build to the normal operating range.

Cover the brake pedal with your foot and depress both the yellow and red brake buttons. Wait a few seconds to allow the truck to settle against the chocks. Press and hold the brake pedal down as far as you can for a full minute. Watch the air gauges and monitor the amount of pressure loss. The system should not lose more the 3 psi during this test.

Begin pumping the brake pedal. You will hear air being expelled from the system with each pump of the brakes and you should be watching the primary and secondary air gauges on the dash. As the air pressure decreases, the needles on these gauges will fall. As the air pressure begins to fall below the safe threshold, a warning buzzer will sound and an indicator light on the dash will begin to blink. Continue to pump the brake pedal. Once the needle on the primary gauge falls to approximately 90 psi, the red trailer brake button should pop out. Continue pumping the pedal, and as the pressure continues to drop, the yellow tractor button will pop out.

Allow the air system to pressurize again, then set the parking brakes. Although the transmission should not have been engaged at any point during these tests, take a moment to make sure that the truck is not in gear. Retrieve the tire chocks.


Drain the air tanks reservoir every few days to remove any collected water. Water in the air lines caused by condensation can prevent the brake system from performing properly.


Always perform air brake system checks on level pavement and away from traffic.

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