Hawaii Air Brakes CDL Practice Test

This is a free 20-question practice test for the Air Brakes portion of the Hawaii 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 Hawaii Driver License Office 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 Hawaii.

Question 1 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 2 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 3 of 20

Air storage tanks are used to:

Carry coolant
Hold compressed air for use by the brakes
Store fuel
House the alternator

Correct. Air storage (or "supply") tanks hold compressed air ready for brake application. Trucks have multiple tanks for redundancy.

Question 4 of 20

The "brake-system warning device" must come on no later than:

10 psi
30 psi
60 psi
100 psi

Correct. A federal-rule low-air-pressure warning device must activate at or before 60 psi.

Question 5 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 6 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 7 of 20

The supply pressure gauges show:

The brake-pedal pressure
The pressure in the air storage tanks
The amount of air being used by the brakes
The trailer brake pressure only

Correct. The supply (primary and secondary) pressure gauges show air pressure available for braking — a critical reading before driving and during operation.

Question 8 of 20

The governor controls:

Engine RPM
When the air compressor pumps air into the air storage tanks
Brake-pedal travel
Trailer hand-valve operation

Correct. The governor cycles the compressor: it cuts the compressor in around 100 psi and cuts it out around 125 psi.

Question 9 of 20

The spring brakes:

Are held off by air pressure and apply automatically when pressure drops
Are activated only by the foot valve
Are activated only by the trailer hand valve
Are not used in modern trucks

Correct. Spring brakes use heavy springs that apply the brake when air pressure is released or drops below 20-45 psi — they serve as both parking and emergency brake.

Question 10 of 20

A condition called "brake fade" is most likely on:

Long downgrades
Flat highway
Backing into a dock
Fueling

Correct. Brake fade comes from heat from extended use — most commonly on long, steep downgrades where the brakes are working continuously.

Question 11 of 20

In a fully charged dual air-brake system at idle, you should test the low-pressure warning by:

Letting the air bleed down with the engine off and brakes off, fanning the brakes if needed; warning should activate at or before 60 psi
Holding the foot valve down for one minute
Removing the alternator belt
Disconnecting the compressor

Correct. Engine off, fan the brake pedal to bleed pressure. The low-pressure warning device should activate before pressure drops below 60 psi.

Question 12 of 20

When should you NOT use the parking brakes?

When the vehicle is parked
When the brakes are very hot, such as after a long downgrade — they could damage if applied
At any time
When the engine is off

Correct. Hot brakes can be damaged by the spring brakes contracting against hot drums. Let the brakes cool before parking.

Question 13 of 20

The parking-brake control:

Is a yellow diamond-shaped knob
Is a red round knob
Is a green knob
Does not exist on modern trucks

Correct. The parking-brake control is a yellow diamond-shaped knob, distinct from the red round trailer-supply knob.

Question 14 of 20

In a dual air-brake system, you should let the air pressure build to at least what level before driving?

60 psi
80 psi
100 psi
125 psi

Correct. Wait until the system pressure is at least 100 psi before driving in a dual air-brake system.

Question 15 of 20

Stopping distance for a vehicle with air brakes is the sum of:

Perception distance + reaction distance + brake-lag distance + braking distance
Brake-lag only
Reaction time only
Braking distance only

Correct. Air-brake stopping distance is perception + reaction + brake lag + braking — the brake lag is the unique addition.

Question 16 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 17 of 20

Air brakes take longer to work than hydraulic brakes because:

Air takes longer to flow than fluid
Air-brake lines are longer than hydraulic lines and have more components
Drivers wait longer to brake
Air brakes are simpler

Correct. Brake-lag in air systems comes from the time air takes to travel through lines and reach all the brake chambers — typically 0.4 seconds added to perception/reaction time.

Question 18 of 20

Pre-trip air-brake check (Step 1) is to:

Test the parking brake
Test the air leakage rate
Time the air-pressure build-up
Check the slack adjusters

Correct. In the seven-step air-brake check the first step is testing the parking brake — release service brakes, set parking brake, gently try to move the vehicle in low gear.

Question 19 of 20

On a vehicle with ABS, in an emergency stop you should:

Pump the brakes
Apply the brakes the way you always would and steer where you need to go
Apply the parking brake
Coast

Correct. ABS lets you brake hard and continue steering. Brake firmly and avoid pumping — pumping defeats the system.

Question 20 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.

About the Hawaii 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 Hawaii Driver License Office 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 Hawaii CDL practice tests.