Oak Tree Technical

CDL Air Brake Check

A guide to performing Air Brake Checks

  1. Performing Tug Tests
    Tug against parking brake only. Tug against emergency brake only. Test Service brake by accelerating to 5 mph and pressing the brake pedal. If the vehicle pulls to one side, this indicates a brake alignment problem.
  2. EngineOn / Brakes On
    Checking the air pressure gauges to make sure they are rising to governor cut off or 120 PSI to 140 PSI. Governor cut off happened at xx PSI.
  3. Engine Off / Key On
    Push in brake valves and after initial drop, I’ll hold my brake pedal for 1 minute and should lose no more than 3 PSI for a B truck and 4 PSI for an A truck. (This portion of the air brake test is checking for leaks as if you were stopped at a light with your foot on the brake).
  4. Key Still On / Engine Still Off / Brake Still Off
    I will pump my brakes until the pressure drops. Warning: the low air warning device should sound and/or appear on dash at, or above 55 PSI. My warning light and buzzer came on at 55 PSI.
  5. Continue Pumping the brakes to between 20 and 40 PSI where the brake valves should pop out applying the brakes. My brake valves popped at xx PSI.


    If there is a problem discovered while testing the Air Brakes, do not drive the vehicle. It is your responsibility to make sure it is repaired by a mechanic. Never operate a vehicle that is unsafe to drive.