Arizona Air Brakes CDL Practice Test

This is a free 20-question practice test for the Air Brakes portion of the Arizona 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 Arizona Motor Vehicle Division 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 Arizona.

Question 1 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 2 of 20

The S-cam:

Is a type of fuel pump
Forces the brake shoes against the drum to provide braking action
Adjusts the slack adjuster
Is the parking-brake control

Correct. When the foot valve is pressed, air pushes the brake-chamber pushrod, which moves the slack adjuster, which rotates the S-cam shaft, forcing the shoes against the drum.

Question 3 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 4 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 5 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 6 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 7 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 8 of 20

In an emergency stop on a non-ABS vehicle, you should:

Apply the brakes lightly
Use stab braking — full brake until wheels lock, release, repeat
Pump the brakes rapidly
Apply only the trailer hand valve

Correct. Stab braking applies brakes hard until the wheels lock, then releases when you feel skid — this slows the vehicle while keeping it straight.

Question 9 of 20

Modern trucks have ABS that is required on:

Tractors built after March 1, 1998 and trailers built after March 1, 1998
All trucks
Only school buses
Only doubles

Correct. Federal rule: tractors built after March 1, 1997, and trailers and single-unit air-braked vehicles after March 1, 1998, must have ABS.

Question 10 of 20

You hear a steady "ssss" sound while parked with the engine off. This is most likely:

Normal venting
An air leak that needs immediate attention
The compressor running
Trailer brakes releasing

Correct. A steady hiss with the engine off indicates an air leak — find and repair before driving.

Question 11 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 12 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 13 of 20

Which of these is the safest speed for descending a long, steep grade?

The posted speed limit
A speed slow enough that the brakes can hold without overheating, typically below the speed limit
Whatever speed you went up the hill
Maximum gear-down speed

Correct. Choose a speed and gear that lets the brakes work intermittently without continuous pressure. Posted truck-grade signs help.

Question 14 of 20

When the spring brakes apply automatically as air pressure drops, this typically happens between:

100 and 120 psi
60 and 80 psi
20 and 45 psi
5 and 10 psi

Correct. Spring brakes will fully apply somewhere between 20 and 45 psi as system pressure drops, depending on the vehicle.

Question 15 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 16 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 17 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 18 of 20

You should perform a static air-leakage test by:

Driving and watching the gauge
With the engine off, brakes released, watching air pressure for one minute
With the engine running at high RPM
By tapping the air tank with a wrench

Correct. Engine off, brakes released, fully charged system: watch for air loss over one minute. Then apply brakes and check again.

Question 19 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.

Question 20 of 20

You should test the parking brake by:

Pushing on it
Setting it, releasing service brakes, and gently trying to move the vehicle in low gear — it should hold
Driving without it
Banging on it with a hammer

Correct. After applying the parking brake and releasing the service brakes, gently try to move forward in low gear. If the vehicle moves, the parking brake is not holding.

About the Arizona 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 Arizona Motor Vehicle Division 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 Arizona CDL practice tests.