Colorado CDL — Air Brakes Exam Simulation
25 questions · 20 correct to pass. You won't see any feedback until you finish — just like the real test.
Colorado CDL — Air Brakes questions with answers
20 sample questions from the Colorado CDL — Air Brakes question bank — each with the correct answer, a short explanation, and the section of the official handbook it comes from.
1. What condition of the brake linings should cause you to reject the vehicle during inspection?
Correct answer: Linings soaked with oil or grease, or worn dangerously thin
Linings must not be loose, soaked with oil or grease, or dangerously thin, and mechanical parts must be in place and not broken or missing.
Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.3.2 - Walk-around Inspection
2. On large buses, at what pressure do low air pressure warning devices commonly activate?
Correct answer: 80 to 85 psi
It is common for large buses to have their low-pressure warning signal come on earlier, in the 80 to 85 psi range.
Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.1.11 - Low Air Pressure Warning
3. On a vehicle with dual parking control valves and a separate air tank, what limits how you use it to move after the main air is lost?
Correct answer: The separate tank holds only enough air for a few releases
The separate reservoir holds only enough air to release the spring brakes a few times, so you must plan your move carefully or risk stopping in a bad spot.
Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.1.15 - Parking Brake Controls
4. On a long, steep downgrade, how should you think about your brakes?
Correct answer: As a supplement to the braking effect of the engine
The brakes are only a supplement to the engine's braking effect; you should already be in the proper low gear before using them on a grade.
Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.4.6 - Proper Braking Technique
5. On newer air brake vehicles, how do you apply the parking brakes?
Correct answer: Pull out the yellow, diamond-shaped knob
You pull out the yellow, diamond-shaped push-pull knob to set the parking (spring) brakes and push it in to release them.
Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.1.15 - Parking Brake Controls
6. Which brake problem is described as the most common one found during roadside inspections?
Correct answer: Brakes that are out of adjustment
Out-of-adjustment brakes are the most common problem found in roadside inspections, and vehicles with too much slack can be very hard to stop.
Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.3.2 - Walk-around Inspection
7. Air-braked truck-tractors built on or after which date are required to have anti-lock brakes?
Correct answer: March 1, 1997
The requirement applies to truck-tractors with air brakes built on or after March 1, 1997 (other air-braked vehicles were required on or after March 1, 1998).
8. Why should you avoid pressing and releasing the brake pedal more than necessary?
Correct answer: It can drain air faster than the compressor can restore it, leaving too little pressure to brake
Each release lets compressed air escape; pumping the pedal can bleed air faster than the compressor can replace it, and if pressure drops too low the brakes stop working.
Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.1.7 - The Brake Pedal
9. What does the supply pressure gauge in the cab tell the driver?
Correct answer: How much air pressure is in the tanks
This gauge reports how much air pressure is currently stored in the tanks; a dual system has one for each half.
Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.1.9 - Supply Pressure Gauges
10. If the low air pressure warning comes on and pressure keeps falling, why can a heavily loaded vehicle need a long distance to stop?
Correct answer: Because the spring brakes do not work on all of the axles
When pressure drops into the 20 to 45 psi range the spring brakes apply, but they do not work on every axle, so a heavy load takes a long distance to stop.
Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.4.7 - Low Air Pressure
11. What is "brake lag" in an air brake system?
Correct answer: The delay before air reaches the brakes after you press the pedal
Brake lag is the short delay (about half a second or more) it takes for air to travel through the lines and make the brakes work after you press the pedal.
Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.4.4 - Stopping Distance
12. What should you always do before leaving your vehicle unattended?
Correct answer: Apply the parking brakes or chock the wheels
Never leave the vehicle unattended without applying the parking brakes or chocking the wheels, or it could roll away and cause harm.
Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.4.8 - Parking Brakes
13. During the engine-compartment inspection of a belt-driven air compressor, what should you check?
Correct answer: That the drive belt is in good condition and properly tight
If the compressor is belt-driven, check that the drive belt is in good condition and properly tight.
Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.3.1 - Engine Compartment Checks
14. When testing the low pressure warning signal, before what pressure must the warning turn on?
Correct answer: Before pressure drops below 55 psi
As you fan down the tank pressure, the low air warning must come on before pressure falls below 55 psi (or the lowest tank in a dual system).
Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.3.3 - Final Air Brake Check
15. What causes brakes to fade from excessive heat?
Correct answer: Overheating that reduces lining friction and expands the drums
Overusing the service brakes overheats them; the heat changes the lining chemically to reduce friction and expands the drums so the shoes must reach farther with less force.
Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.4.5 - Brake Fading or Failure
16. Total stopping distance for an air-braked vehicle is made up of how many factors?
Correct answer: Four
It adds up from four parts: perception distance, reaction distance, brake lag distance, and braking distance.
Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.4.4 - Stopping Distance
17. Why should you avoid pressing the brake pedal while the spring brakes are already applied?
Correct answer: The combined spring and air forces can damage the brakes
Combining the spring force with added air pressure can damage the brakes, so it is best never to push the pedal while the spring brakes are on.
Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.1.15 - Parking Brake Controls
18. How do you test the service brakes after building normal air pressure?
Correct answer: Move forward slowly, apply the brakes firmly, and note any pulling or delay
Release the parking brake, roll forward slowly (at least about five mph), and apply the brakes firmly, watching for pulling to one side, odd feel, or delayed stopping.
Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.3.3 - Final Air Brake Check
19. What color is the ABS malfunction lamp used to warn of a fault?
Correct answer: Yellow
Vehicles with ABS use yellow malfunction lamps to indicate that something in the anti-lock system is not working.
20. How do spring brakes stay released while you are driving?
Correct answer: Air pressure holds the springs back until the pressure is removed
Powerful springs are held back by air pressure during normal driving; if that air is removed or lost, the springs apply the brakes.
Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.1.14 - Spring Brakes