West Virginia Air Brakes CDL Practice Test

This is a free 20-question practice test for the Air Brakes portion of the West Virginia Commercial Driver's License knowledge exam. Questions are pulled from a pool of 71 drawn from the AAMVA CDL Manual, which is the source document the West Virginia Division of Motor Vehicles uses to write its actual exam.

How it works: Click an answer. The correct choice highlights in green, and you'll see a short explanation. Aim for 85% or better before you sit for the real test in West Virginia.

Question 1 of 20

Air tanks must be drained because:

They get heavy
Compressor oil and water can collect inside, contaminating the brake system
They expire
It is required after every trip

Correct. Water and compressor oil collect at the bottom of air tanks. They must be drained to keep the system clean and prevent winter freeze-ups.

Question 2 of 20

Slack adjusters need to be checked because:

They wear and require adjustment to maintain braking force
They never need attention
They are decorative
They affect only the parking brake

Correct. Slack adjusters control how far the pushrod must travel to apply the brake. Out-of-adjustment slack adjusters are the leading mechanical cause of out-of-service violations.

Question 3 of 20

When should you use the trailer hand valve to slow the rig?

Whenever you want trailer-only braking
Never; using the trailer hand valve alone can cause a trailer skid
Always when going downhill
Only on dry pavement

Correct. Using the trailer hand valve alone applies brakes only at the trailer wheels and can cause the trailer to lock up and skid. Always use the foot valve to brake.

Question 4 of 20

The trailer air-supply control:

Is a yellow diamond knob
Is a red eight-sided (octagonal) knob
Is a green knob
Is the same knob as the parking brake

Correct. The trailer air-supply (tractor protection) is a red eight-sided knob. Push in to supply air to the trailer; pull out to shut off air.

Question 5 of 20

Brake fade is the result of:

Cold brakes
Worn linings only
Heat from continuous use, which reduces braking effectiveness
Air leaks

Correct. Brake fade comes from heat. Manage downgrade speed by gear selection plus intermittent firm brake use, not continuous light pressure.

Question 6 of 20

After connecting the trailer air lines, you should:

Drive away
Charge the trailer air system, check that the trailer brakes work, and inspect glad-hand connections
Lock the trailer brakes
Turn off the supply

Correct. Charge the trailer system, then test the trailer brakes by pulling out the trailer-supply knob to make sure they hold the trailer.

Question 7 of 20

When you make a normal stop with air brakes, you should:

Push the brake pedal down hard
Apply firm steady pressure to slow you smoothly
Pump the brakes
Use only the trailer brake

Correct. For normal stops, apply steady firm pressure on the foot valve and adjust to maintain a smooth stop.

Question 8 of 20

For a single vehicle with engine off and brakes applied, the maximum allowable air-loss rate is:

1 psi/min
2 psi/min
3 psi/min
4 psi/min

Correct. A single vehicle is allowed no more than 3 psi/min with brakes fully applied.

Question 9 of 20

Air loss from the brake system on a moving combination vehicle, with brakes applied, should not exceed:

2 psi/min
3 psi/min
4 psi/min
6 psi/min

Correct. Combination vehicle, brakes applied, engine off: no more than 4 psi/min air loss. Engine off, brakes released: no more than 3 psi/min.

Question 10 of 20

The "tractor protection valve" closes (cuts off air to the trailer) automatically when:

You apply the brakes
Air pressure in the tractor drops to a dangerously low level (typically 20 to 45 psi)
You hit a bump
You shift gears

Correct. The tractor protection valve protects the tractor from a runaway air loss in case of a trailer break-away or air leak — it closes between 20 and 45 psi.

Question 11 of 20

You should never leave the vehicle unattended without:

Locking the doors
Applying the parking brakes and chocking the wheels if necessary
Turning off the radio
Removing the key

Correct. Set the parking brake. On grades or where unintended movement could occur, chock the wheels in addition.

Question 12 of 20

To check air-brake adjustment quickly, you can:

Measure the slack adjuster pushrod travel; if it has moved more than about 1 inch when brakes are applied at 90+ psi, adjustment is needed
Listen to the sound
Look at the tires
Check the dashboard light

Correct. Pushrod travel beyond about 1 inch (varies by chamber size) indicates an adjustment issue. Use a marked stroke check or have a mechanic verify.

Question 13 of 20

When brake drums or shoes get very hot, you should:

Park immediately
Continue driving
Pull over and let them cool, but do not apply the parking brake until they have cooled
Throw water on them

Correct. Park where you can let the brakes cool. Do not apply the parking (spring) brake on overheated brakes — it can damage them or cause warpage.

Question 14 of 20

The parts of an air-brake system include:

Air compressor, governor, air storage tanks, foot valve, and brake chambers
Master cylinder, brake fluid, and calipers
Hydraulic pump, lines, and disc rotors
Vacuum booster and reservoir

Correct. Air-brake systems use a compressor, governor, storage tanks, foot valve, and brake chambers — distinct from hydraulic systems used in cars.

Question 15 of 20

You are driving a fully loaded combination vehicle on a steep downgrade. Your safe speed is 30 mph and you have already shifted to a lower gear. The proper braking technique is to:

Hold the brakes lightly the whole way
Apply firmly to slow to 25 mph (5 mph below safe speed), release, and let speed build back to 30, then repeat
Stay at 30 mph
Apply only the trailer brake

Correct. The "snub-and-release" method: brake firmly to drop 5 mph below safe speed, release until safe speed returns, repeat. Holding the brakes overheats them.

Question 16 of 20

The application pressure gauge shows:

The pressure in the storage tanks
How much pressure is being applied to the brakes when you press the foot valve
Tire pressure
Engine oil pressure

Correct. The application gauge (when present) shows brake-application pressure — useful for spotting brake-system problems on long downgrades.

Question 17 of 20

Air-brake adjustment is critical because out-of-adjustment brakes:

Reduce stopping power and can cause failure on long downgrades
Improve fuel economy
Have no effect
Require less air pressure

Correct. Out-of-adjustment slack adjusters reduce braking force at the wheel, increasing stopping distance and risking brake failure on long downgrades.

Question 18 of 20

In a dual air-brake system, the time required for air pressure to build from 85 to 100 psi should be no more than:

15 seconds
30 seconds
45 seconds
120 seconds

Correct. In dual air-brake systems, air should build from 85 to 100 psi within 45 seconds at engine governed RPM.

Question 19 of 20

For a combination vehicle (tractor and trailer) with engine off and brakes released, the maximum allowable air-loss rate is:

2 psi/min
3 psi/min
4 psi/min
6 psi/min

Correct. A combination vehicle is allowed no more than 3 psi/min with brakes released, or 4 psi/min with brakes applied.

Question 20 of 20

A yellow ABS malfunction lamp on the cab dash means:

Everything is fine
The ABS on the tractor is malfunctioning
The trailer ABS is malfunctioning
Air pressure is low

Correct. A yellow ABS lamp on the dash indicates a tractor-ABS malfunction. The base brakes still work normally, but ABS is unavailable until repaired.

About the West Virginia Air Brakes exam

States typically administer 25 Air Brakes questions and require 80% to pass. Questions cover air-brake system parts, dual systems, supply pressure, brake-system warning, slack adjusters, the parking brake, the spring brake, the pre-trip air-system check, and the proper way to perform a leakage-rate test.

The West Virginia Division of Motor Vehicles follows the federal CDL standards established by FMCSA. To earn the Air Brakes credential, you must answer at least 80% of the questions correctly. Many candidates score lower the first time because the test pulls from a large pool — refreshing this page will give you a different mix of questions, drawn from the same authoritative source.

Want more practice? Try the full Air Brakes question bank or browse all West Virginia CDL practice tests.