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Key Facts: NC CDL Air Brakes Exam

80%

Minimum score on each North Carolina CDL knowledge test, including air brakes

N.C. CDL Manual Section 1.1.1; 49 CFR 383.135

$51.50

Nonrefundable CDL application fee covering three knowledge test attempts

N.C.G.S. 20-37.15(a1)

1 per day

Attempts allowed at each CDL knowledge test

N.C. CDL Manual Section 1.1.1

60 psi

Pressure before which the low air pressure warning must come on

N.C. CDL Manual Section 5.1.11

20-45 psi

Range in which tractor and straight truck spring brakes come fully on

N.C. CDL Manual Section 5.1.14

45 seconds

Maximum time for a dual air system to build from 85 to 100 psi at operating rpm

N.C. CDL Manual Section 5.3.3

North Carolina CDL applicants whose vehicles have air brakes, including air over hydraulic brakes, must pass the Air Brakes knowledge test with at least 80 percent correct or receive an L restriction (N.C. CDL Manual Section 1.1.1; 49 CFR 383.95). NCDMV allows one attempt per knowledge test per day, and the $51.50 application fee covers three attempts (G.S. 20-37.15(a1)). The N.C. manual still uses the July 2014 AAMVA text: the governor cuts in at about 100 psi and out at about 125 psi, the safety valve opens at about 150 psi, the low air warning must come on before 60 psi, and spring brakes come fully on at 20-45 psi. Dual systems should build from 85 to 100 psi within 45 seconds, and leakage must stay under 2 psi per minute (single) or 3 psi (combination) with brakes released, and no more than 3 or 4 psi with brakes applied.

Sample NC CDL Air Brakes Practice Questions

Try these sample questions to review concepts for the NC CDL Air Brakes exam. Each question includes a detailed explanation. Start the interactive quiz above for the full 220+ question experience with AI tutoring.

1Under Section 1.1.1 of the N.C. Commercial Driver License Manual, which CDL applicants must take the air brakes knowledge test?
A.Only Class A applicants who will pull a trailer equipped with air brakes
B.Only applicants whose vehicle has full air brakes; air over hydraulic systems are exempt
C.Any applicant whose vehicle has air brakes, including air over hydraulic brakes
D.Only applicants who are seeking a passenger or school bus endorsement
Explanation: Section 1.1.1 lists the air brakes test as one you must take if your vehicle has air brakes, including air over hydraulic brakes. The requirement follows the brake system, not the license class or endorsement, and Figure 1.2 tells applicants to study Section 5 if they plan to operate vehicles equipped with air brakes.
2A North Carolina applicant passes the general knowledge test but fails the air brakes knowledge test, and a commercial learner's permit is issued. Which restriction must the permit carry?
A.L (no air brake equipped CMV)
B.Z (no full air brake equipped CMV)
C.E (no manual transmission CMV)
D.K (intrastate only)
Explanation: Under 49 CFR 383.95(a), which the N.C. manual repeats, an applicant who does not take or fails the air brake component of the knowledge test gets the L restriction on the CLP or CDL. L bars operating a CMV with any type of air brakes, including systems that work only partly on the air brake principle.
3A driver passed the N.C. air brakes knowledge test and then took the CDL skills test in a truck with air over hydraulic brakes. Which statement describes the resulting CDL?
A.It carries an L restriction, so the driver may not operate any CMV with air brakes
B.It carries no brake restriction, because the knowledge test was passed
C.It carries an E restriction until a second skills test is taken in a full air brake vehicle
D.It carries a Z restriction: air over hydraulic CMVs are allowed, full air brake CMVs are not
Explanation: When the skills test is performed in a vehicle with air over hydraulic brakes, the state must show the Z restriction (no full air brake equipped CMV) under 49 CFR 383.95(b) and the N.C. manual. The driver may still operate CMVs whose brakes work partly on the air principle, but not those operating fully on air brakes.
4An applicant passes the air brakes knowledge test but takes the skills test in a straight truck that has hydraulic brakes only. According to the N.C. manual, what happens?
A.No restriction is added, because the written air brakes test was passed
B.The CDL carries an L restriction, barring CMVs with any type of air brakes
C.The CDL carries a Z restriction, allowing air over hydraulic CMVs only
D.The CDL is withheld until the skills test is repeated in an air brake vehicle
Explanation: The L restriction is triggered either by failing or skipping the air brake knowledge test or by performing the skills test in a vehicle not equipped with air brakes. Section 1.1.2 says that to operate a vehicle with air brakes you must pass the written air brake test and pass a skills test in an air brake-equipped vehicle.
5Which combination lets a new North Carolina CDL holder drive CMVs with full air brakes, with no L or Z restriction?
A.Pass the air brakes knowledge test and take the skills test in an air over hydraulic vehicle
B.Take the skills test in a full air brake vehicle without taking the air brakes knowledge test
C.Pass the air brakes knowledge test and take the skills test in a vehicle with full air brakes
D.Pass the air brakes knowledge test; the brakes on the skills test vehicle do not matter
Explanation: Both parts matter. Failing or skipping the air brake knowledge test produces L, a skills test in a vehicle without air brakes produces L, and a skills test in an air over hydraulic vehicle produces Z. Only passing the knowledge test and testing in a full air brake vehicle avoids both restrictions (49 CFR 383.95; N.C. manual Section 1.1.2).
6Under Section 1.1.1 of the N.C. CDL manual, how often may you attempt the same CDL knowledge test, such as air brakes?
A.As often as you like on the same day, until the office closes
B.Twice per day, with a 30-minute wait between attempts
C.Once every seven days after a first failure
D.Only one attempt at each knowledge test per day
Explanation: Section 1.1.1 states that only one attempt at each knowledge test is allowed per day and that 80 percent of the questions must be answered correctly to pass each test. No appointment is needed for knowledge tests, and the CDL application fee covers three attempts before another application fee is required.
7Section 5 of the N.C. manual splits an air brake setup into three braking systems by function. Which list names them?
A.Primary, secondary, and trailer systems
B.Service, parking, and emergency systems
C.Foundation, spring, and antilock systems
D.Supply, control, and relay systems
Explanation: Section 5 explains that air brakes are really three systems: the service brake (applied and released with the brake pedal in normal driving), the parking brake (applied with the parking brake control), and the emergency brake. The emergency system uses parts of the service and parking systems to stop the vehicle if the brake system fails.
8How does the N.C. CDL manual describe the emergency brake system on an air-braked vehicle?
A.It uses parts of the service and parking systems to stop the vehicle if the brakes fail
B.A separate set of air tanks and brake chambers reserved for emergencies, isolated from the service brakes
C.The trailer hand valve, which the driver uses to stop when the foot brake fails
D.An engine retarder that engages automatically when air pressure is lost
Explanation: Per Section 5, the emergency brake system uses parts of the service and parking brake systems to stop the vehicle in a brake system failure. Spring brakes, which the parking control also uses, are the usual way trucks, tractors, and buses meet the emergency brake requirement.
9Some air compressors have their own oil supply instead of using engine oil. What does the N.C. manual tell you to do with this type?
A.Drain the compressor oil at the end of each day along with the air tanks
B.Add a small amount of alcohol to the compressor oil in cold weather
C.Check the compressor oil level before driving
D.Nothing, because compressors with their own oil are sealed for life
Explanation: Section 5.1.1 says the compressor is connected to the engine through gears or a v-belt, may be air cooled or cooled by the engine cooling system, and may have its own oil supply or use engine oil. If it has its own oil supply, check the oil level before driving.
10With the engine running, you watch the air gauge climb. At about what reading should the governor cut out so the compressor stops pumping air into the tanks?
A.About 60 psi
B.About 100 psi
C.About 150 psi
D.About 125 psi
Explanation: Section 5.1.2 states that the governor stops the compressor when tank pressure rises to the cut-out level, around 125 psi, and lets it pump again when pressure falls to the cut-in level, around 100 psi. Check the manufacturer's specifications for the exact values on your vehicle.

About the NC CDL Air Brakes Exam

The North Carolina CDL Air Brakes knowledge test is required for any applicant whose commercial vehicle has air brakes, including air over hydraulic brakes. NCDMV gives it at driver license offices, and Section 5 of the N.C. Commercial Driver License Manual is its study section; you need 80 percent correct, and NCDMV does not publish the number of questions. Failing or skipping the test puts an L restriction on the CLP or CDL, and taking the skills test in an air over hydraulic vehicle adds a Z restriction. Independent practice by OpenExamPrep covers the compressor and governor, tanks and drains, foundation brakes, the 60 psi low air warning, spring brakes, ABS, dual systems, inspection and leakage limits, emergency and downgrade braking, and trailer air lines. These four-option questions are a study aid, not the official NCDMV test, and they do not replace the hands-on air brake check on the skills test.

Exam sponsor: North Carolina Division of Motor Vehicles (NCDMV), N.C. Department of Transportation. The requirements and fees below concern the certification or admission exam, separate from our free practice resources.

Assessment

A multiple-choice knowledge test at an NCDMV driver license office, taken with your other CDL knowledge tests before the commercial learner's permit is issued. To drive air-braked CMVs without an L or Z restriction, you must also take the skills test in a vehicle with full air brakes. Its vehicle inspection includes a three-part air brake check (applied leakage, low air warning, and parking brake/tractor protection valve pop-out), and doing it incorrectly is an automatic failure.

Time Limit

Not published by NCDMV

Passing Score

80% on each CDL knowledge test

Exam / Certification Fees

$51.50 nonrefundable CDL application fee covering three knowledge test attempts (G.S. 20-37.15(a1)); no separate air brakes test fee. The CDL costs $25.50 per year plus $5.00 per endorsement per year (G.S. 20-37.16(d)).

Exam sponsor website

Fees, eligibility, and exam policies can change. Confirm them with the exam sponsor before applying or paying.

Our practice resources: topics covered

We aim to reflect publicly available exam outlines and topic information in our study resources. Coverage, format, and difficulty may differ from the actual exam, and we cannot guarantee that every detail is accurate or current. Confirm exam requirements, fees, and policies with the official exam sponsor.

Manual Sections 1.1.1-1.1.2 and the L/Z restriction codes (official weight not published)

Air Brake Testing and Restrictions

Who must take the air brakes test, the 80% passing rule, one attempt per test per day, and how the knowledge test and the skills test vehicle decide the L (no air brakes) and Z (no full air brakes) restrictions.

Manual Sections 5.1.1-5.1.13 (official weight not published)

Air Brake System Parts

Service, parking, and emergency systems; compressor and governor (cut-in about 100 psi, cut-out about 125 psi); tanks, drains, alcohol evaporator, and the 150 psi safety valve; s-cam, wedge, and disc brakes; supply and application gauges; the 60 psi low air warning and wig wag; stop light switch; front brake limiting valves.

Manual Sections 5.1.14-5.1.15 and 5.4.8 (official weight not published)

Spring Brakes and Parking Controls

Spring brakes coming fully on at 20-45 psi (typically 20-30 psi), the yellow diamond parking knob, modulating and dual parking control valves, and when not to use the parking brakes.

Manual Sections 5.1.16, 5.4.2, and 2.18 (official weight not published)

Antilock Braking Systems

ABS dates (air-braked truck tractors from March 1, 1997; other air-braked vehicles from March 1, 1998), malfunction lamps, braking with ABS on the tractor only or the trailer only, and what ABS cannot do.

Manual Section 5.2 (official weight not published)

Dual Air Brake Systems

Primary and secondary systems, building at least 100 psi in both before driving, the warning shut-off value above 60 psi, and losing pressure in one system.

Manual Section 5.3 and the Section 11 air brake check (official weight not published)

Inspecting Air Brakes

Seven-step inspection add-ons, slack adjusters (about one inch), drums and linings, low air warning and spring brake tests, build-up rates, leakage limits, governor checks, parking and service brake tests, and the three-part skills-test air brake check.

Manual Sections 5.4 and 2.16 (official weight not published)

Using Air Brakes

Normal and emergency stops, controlled and stab braking, brake lag (one half second or more; about 32 feet at 55 mph; total stopping distance over 450 feet), brake fade, the downgrade braking technique, and low air pressure.

Manual Section 6.2; 49 CFR 383.111(b)(3) (official weight not published)

Trailer Air Lines and Tractor Protection

The tractor protection valve, red trailer air supply control, service and emergency lines, glad hands, and the trailer hand valve. Federal rules list the effects of severed or disconnected trailer air lines among the required air brake knowledge areas.

Preparing for the NC CDL Air Brakes Exam

What You Need to Know

  • Passing score: 80% on each CDL knowledge test
  • Assessment: A multiple-choice knowledge test at an NCDMV driver license office, taken with your other CDL knowledge tests before the commercial learner's permit is issued. To drive air-braked CMVs without an L or Z restriction, you must also take the skills test in a vehicle with full air brakes. Its vehicle inspection includes a three-part air brake check (applied leakage, low air warning, and parking brake/tractor protection valve pop-out), and doing it incorrectly is an automatic failure.
  • Time limit: Not published by NCDMV
  • Exam / certification fees: $51.50 nonrefundable CDL application fee covering three knowledge test attempts (G.S. 20-37.15(a1)); no separate air brakes test fee. The CDL costs $25.50 per year plus $5.00 per endorsement per year (G.S. 20-37.16(d)). Official sources

Using Our Practice Resources

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NC CDL Air Brakes: Suggested Study Strategy

1Memorize the N.C. manual's pressures: governor cut-in about 100 psi, cut-out about 125 psi, safety valve about 150 psi, low air warning before 60 psi (80-85 psi on large buses), and spring brakes at 20-45 psi.
2Know the leakage limits: brakes released, under 2 psi per minute single or 3 psi combination; brakes applied for one minute, no more than 3 psi single or 4 psi combination.
3Practice the three-part skills-test air brake check in order: applied leakage, low air warning, then parking brake and tractor protection valve pop-out.
4Learn what triggers each restriction: L for failing or skipping the knowledge test or testing without air brakes, Z for testing in an air over hydraulic vehicle.
5For brake lag, remember one half second or more, about 32 feet at 55 mph, and a total stopping distance over 450 feet.
6Do not set the parking brakes when the brakes are very hot or very wet in freezing weather; chock the wheels instead.

Frequently Asked Questions

Who must take the North Carolina CDL air brakes test?

Section 1.1.1 of the N.C. CDL Manual says you must take the air brakes test if your vehicle has air brakes, including air over hydraulic brakes. If you fail or skip it, the CLP or CDL carries an L restriction that bars any CMV with air brakes.

How many questions are on the North Carolina CDL Air Brakes test, and what is the passing score?

NCDMV does not publish the number of questions or a time limit for the Air Brakes knowledge test. The N.C. CDL Manual requires 80 percent correct on each CDL knowledge test, which matches the federal standard in 49 CFR 383.135.

What is the difference between the L and Z restrictions in North Carolina?

L (no air brake equipped CMV) is added if you fail or skip the air brake knowledge test or take the skills test in a vehicle without air brakes. Z (no full air brake equipped CMV) is added if you take the skills test in a vehicle with air over hydraulic brakes. To avoid both, pass the knowledge test and test in a full air brake vehicle.

How often can I retake the air brakes knowledge test in North Carolina?

Section 1.1.1 allows only one attempt at each knowledge test per day. The $51.50 application fee covers three attempts, and each further set of three attempts requires another application fee. Passing scores stay valid in NCDMV files for 90 days.

When must the low air pressure warning come on under the N.C. manual?

The N.C. manual says a visible warning must come on before tank pressure falls below 60 psi, or one half the governor cutout pressure on older vehicles. On large buses the warning commonly signals at 80-85 psi.

What are the allowable air leakage rates?

With the engine off and the parking brake released, the loss should be less than 2 psi per minute for a single vehicle and less than 3 psi per minute for a combination. With the foot brake fully applied for one minute, the drop must not exceed 3 psi (single) or 4 psi (combination).

What is the air brake check on the North Carolina skills test?

Section 11 lists three parts: an applied leakage test after building pressure to governor cutoff (120-140 psi), fanning the pedal until the low air warning comes on before 60 psi, and continuing until the parking brake valve (and the tractor protection valve on a tractor-trailer) pops out at about 40 psi. Failing to do all three correctly is an automatic failure of the vehicle inspection test.

Is this practice question bank an official NCDMV test?

No. This is independent practice by OpenExamPrep based on the N.C. Commercial Driver License Manual. Its four-option multiple-choice questions are a study aid; they are not NCDMV test items, and they do not replace hands-on air brake training or the skills test.