# Free District of Columbia CDL Air Brakes Practice Test 2023

Do you need an Air Brakes endorsement or an L endorsement for your commercial driving license? The District of Columbia CDL Air Brake has some differences from other endorsements because your license will receive a mark of restriction if you fail the test. So having good preparation before exam day is very necessary. To ensure that our DC CDL practice test questions are relevant, all of them are based on the DC CDL Manual. Each question has a detailed explanation for you to thoroughly learn the format and the topic. Don't be afraid of having a restriction on your license. Let’s try with our CDL practice test to get ready to pass the District of Columbia CDL Air Brake Test now.

Our CDL practice tests:
Based on 2021 DC commercial driver's license manual
Full answers + detailed explanations
Perfect for first-time, renewal applicants
DC CDL Air Brakes Test format:
25 questions
20 correct answers to pass
80% passing score
List of questions
1.
An automatic wig wag will rise out of your view when the pressure in your system rises above what psi?
2.
The parking or emergency brake on a heavy vehicle can only be held in position by something that cannot leak away, like:
3.
A driver needs to be able to see a warning when the air pressure in the service air tanks falls below ______.
4.
The safety valve discharges automatically at the pressure of:
5.
In case of a low air situation, the spring brakes should come on at _____.
6.
Total stopping distance for air brakes is longer than that for hydraulic brakes due to ______ distance.
7.
If your truck has a properly functioning dual air brake system and minimum size air tanks, the air pressure should build up from 85 to 100 psi within how many seconds?
8.
Why drain water from compressed air tanks?
9.
When increased application pressure to maintain the same speed becomes necessary, you should ______.
10.
Which braking system applies and releases the parking brakes when you use the parking brake control?
11.
In most newer vehicles, the parking brake control will be:
12.
"Some air brake systems have an alcohol evaporator. What may happen if you don’t keep the proper level of alcohol?"
13.
What happens when your brake drums get very hot?
14.
After the initial pressure drop, air leakage for single vehicles should be less than:
15.
Besides heat, another cause of brake fade is:
16.
How should you check that your service brakes are working properly?
17.
When inspecting the air brake system, what particular item in the engine compartment should the driver pay specific attention to?
18.
Controlled braking is only possible _________.
19.
If one air system is very low on pressure _______.
20.
Stop light switches are necessary because ________.
21.
You should use the parking brake _____________.
22.
Air tanks should be drained:
23.
To check the air compressor governor's "cut in" and "cut out" pressures you need to _________.
24.
The governor stops the compressor from pumping air at:
25.
On a long or steep downgrade, how should vehicle speed be primarily controlled?