Free CDL Air Brakes Practice Test 2026

Sample questions

5 air brakes practice questions

Each sample shows the correct answer with a plain-language explanation. The full 61-question bank is in the practice run after you pick a state.

1. 1. The service brake system is the air-brake system used for:

   • AEmergency spring application only
   • BTrailer supply only
   • CParking only on grades
   • Normal stopping while driving

   Answer: Normal stopping while driving. Service brakes use controlled air pressure at the brake chambers for everyday slowing and stopping.

2. 2. If the low-air warning activates while driving, you should:

   • AContinue to the next terminal at highway speed
   • Bring the vehicle to a safe stop while you still have control
   • CFan the brakes to empty the tanks faster
   • DShift to neutral and coast

   Answer: Bring the vehicle to a safe stop while you still have control. The warning means pressure is approaching a level where spring brakes may apply and service braking is limited—stop safely.

3. 3. During controlled braking you should keep steering inputs:

   • ADisabled by setting the parking brake
   • BAs large as possible
   • Very small; release if you need a big steer correction or wheels lock
   • DOnly with one hand

   Answer: Very small; release if you need a big steer correction or wheels lock. Controlled braking is maximum braking without lockup. Large steering demands or lockup mean release, then reapply.

4. 4. A service-brake check at about 5 mph with a firm pedal application is looking for:

   • Pulling to one side, unusual feel, or delayed stopping
   • BTrailer hand-valve color
   • CTire tread brand
   • DGovernor cut-out only

   Answer: Pulling to one side, unusual feel, or delayed stopping. Problems found in a low-speed check are safer to discover before highway speeds.

5. 5. To check governor cut-out, run the engine at a fast idle until:

   • ASpring brakes apply
   • BThe safety valve opens at 80 psi
   • CPressure falls to 60 psi
   • Gauges stop rising at about the manufacturer’s cut-out (around 125 psi)

   Answer: Gauges stop rising at about the manufacturer’s cut-out (around 125 psi). Then fan the brakes with the engine idling and confirm cut-in near the specified pressure (often around 100 psi).