Nevada Air Brakes CDL Practice Test

This is a free 20-question practice test for the Air Brakes portion of the Nevada 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 Nevada Department 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 Nevada.

Question 1 of 20

You should check the air-system pressure build-up time during pre-trip:

Yes — 85 to 100 psi within 45 seconds in dual systems at governed RPM
No, it is not part of pre-trip
Only on cold mornings
Only on triple-trailer rigs

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

Question 2 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 3 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 4 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 5 of 20

During a brake check, the brake pedal should not move more than ___ when you push it down hard with the engine off and air pressure built up:

One inch
A few inches
To the floor
Half its travel

Correct. After full charge, holding the foot valve down should produce a firm pedal that moves only a few inches. Pedal sinking to the floor indicates a leak.

Question 6 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 7 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 8 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 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

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 12 of 20

A low-air-pressure warning device must come on at or before:

20 psi
40 psi
60 psi
80 psi

Correct. A federal-mandated low-air-pressure warning (light, buzzer, or wig-wag) must activate at or before 60 psi.

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

Continuous use of the brakes on a long downgrade can cause:

Improved braking
Brake fade — loss of braking effectiveness due to overheating
No effect
Faster wear of the air compressor

Correct. Holding the brakes overheats them and causes brake fade — drums expand and brake compounds lose effectiveness, reducing braking force.

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

Total stopping distance with air brakes equals:

Perception distance + reaction distance + brake-lag distance + effective braking distance
Reaction distance only
Brake-lag distance only
Perception distance + braking distance

Correct. Add brake-lag distance to the standard perception + reaction + braking distance for any vehicle with air brakes.

Question 17 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 18 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 19 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 20 of 20

A long downgrade requires:

Riding the brakes the whole way
Selecting a low gear before starting down and using intermittent firm brake applications
Coasting in neutral
Using the engine brake only

Correct. Pick a low gear before starting down. Use the brakes in firm, intermittent applications: brake to 5 mph below safe speed, release, repeat.

About the Nevada 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 Nevada Department 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 Nevada CDL practice tests.