The last portion of the test requires the driver to build up air pressure again to 120-125 psi, in order to test the service brakes. Service brakes - Before conducting this test, the driver can grab the wheel chocks. This must happen before pressure drops to 20 psi, to ensure the failsafe is in proper working order. To do this, the driver must continue to apply and release pressure on the foot brake until the parking brake knob(s) pop out. To do this, you must apply and release pressure on the foot brake until the audible or visual alarm alerts to a drop in pressure to no more than 60 psi.īuttons - This test confirms the tractor (and trailer, when applicable) parking brakes are in working order. The air pressure cannot drop more than 3 psi for a tractor, and no more than 4 psi for a combination vehicle (aka, tractor with a coupled trailer).Īlarms - You then must confirm the alarms work to alert drivers of a drop in air pressure. After the initial pressure drop, the driver then engages the brake pedal at a steady pressure for 60 seconds. (Some vehicle alarms will not work unless the vehicle's auxiliary power is available.) The next step is to press in the tractor (and trailer, if applicable) parking brake to release it. Leaks - after the wheels are chocked, and the air pressure built up to between 90-125 psi, the driver should leave the vehicle in neutral and cut the engine.

It allows you to confirm the following (these tests are conducted in order): LABS stands for Leaks, Alarms, Buttons, and Service Brake. The LABS test is a method for remembering all the steps to testing the air brake system on a commercial vehicle, which should be done during a pre-trip inspection. ( Read more about the entire pre-trip inspection process in a previous blog post here.) The LABS test There are four steps to take to ensure all areas of the air braking system are working properly. As a student preparing for the pre-trip inspection portion of the CDL test, I need to know the proper procedure for conducting this test.

One critical step in the pre-trip inspection is to make sure your air brakes are in good operating order before hitting the road.

California cdl air brake test