Kansas Air Brakes CDL Practice Test

This is a free 20-question practice test for the Air Brakes portion of the Kansas 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 Kansas Division of Vehicles uses to write its actual exam.

Illustration of an air brake system on a commercial truck's wheel assembly

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 Kansas.

Question 1 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 2 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 3 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 4 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 5 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 6 of 20

Air brakes are actually three brake systems combined:

Service, parking, and emergency
Engine, parking, and trailer
Drum, disc, and engine
None of the above

Correct. A complete air-brake system has the service brake (foot valve), parking brake (spring/yellow knob), and emergency brake (which is the parking brake working off the spring brake when air drops).

Question 7 of 20

You should drain the air tanks:

Once a month
Once a year
At the end of every working day
Never

Correct. Drain all air tanks at the end of each working day to remove water and compressor oil that has condensed in the tanks.

Question 8 of 20

Manual slack adjusters must be adjusted:

Only by a mechanic at the dealership
By the driver, when needed, following manufacturer specifications
Never
Only at the time of vehicle inspection

Correct. Drivers may adjust manual slack adjusters in compliance with manufacturer specifications. Automatic slack adjusters are now standard but still require periodic checking.

Question 9 of 20

Pushing the brake pedal harder makes:

No difference
More air pressure go to the brake chambers
The compressor run faster
The trailer brakes release

Correct. The foot valve modulates air pressure to the brake chambers in proportion to how hard you press the pedal.

Question 10 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 11 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 12 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 13 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 14 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 15 of 20

When checking the brakes on a downgrade, you should:

Use the air-pressure gauge to monitor brake-system pressure for excessive use
Pump the pedal
Drive faster
Ignore the gauge

Correct. Watch the air-pressure gauge. If pressure drops faster than the compressor can recover, brakes are being used too aggressively for the gear selection.

Question 16 of 20

For a single vehicle (not a combination) with engine off and brakes released, 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 2 psi/min of air loss with engine off and brakes released.

Question 17 of 20

The service brakes are operated by:

The yellow parking-brake knob
The red trailer-supply knob
The foot valve (brake pedal)
The hand throttle

Correct. Service brakes are applied by the foot valve / brake pedal. The yellow and red knobs control parking and trailer-supply functions.

Question 18 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 19 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 20 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.

About the Kansas 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 Kansas Division of 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 Kansas CDL practice tests.