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Key Facts: MD CDL Air Brakes Exam

80%

Passing score required on each Maryland CDL knowledge test

Maryland CDL Manual (DL-151) and 49 CFR 383.135

55 psi

Pressure the low air warning must come on before

Maryland CDL Manual (DL-151) Section 5.1.11

20 to 45 psi

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

Maryland CDL Manual (DL-151) Section 5.1.14

4 parts

Parts of the skills-test air brake check; missing any is an automatic failure

Maryland CDL Manual (DL-151) Section 11.1.2

14 days

Minimum wait after a corrected CLP is issued before the skills test when removing the L restriction

Maryland MVA Knowledge Tests page

The Maryland MVA CDL Air Brakes test requires 80% to pass; the MVA does not publish its question count or time limit. Key figures from Maryland's CDL Manual: governor cut-in about 100 psi and cut-out about 125 psi (120 to 140 psi in the skills-test check), low air warning before 55 psi, spring brakes at 20 to 45 psi, and per-minute leakage limits (single vs. combination) of under 2 vs. 3 psi with brakes released and 3 vs. 4 psi with brakes applied.

Sample MD CDL Air Brakes Practice Questions

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

1Maryland's CDL Manual describes air brakes as really being three different braking systems. Which three?
A.Primary, secondary, and trailer brakes
B.Service, parking, and auxiliary retarder brakes
C.Service, parking, and emergency brakes
D.Foundation, spring, and antilock brakes
Explanation: Section 5 of the Maryland CDL Manual (DL-151) says air brakes are really three systems: the service brake (applied with the pedal in normal driving), the parking brake (applied with the parking brake control), and the emergency brake, which uses parts of the other two if the brake system fails.
2If the brake system fails while you are driving, the emergency brake system stops the vehicle. According to Maryland's CDL Manual, what does it use to do that?
A.Parts of the service and parking brake systems
B.A separate hydraulic circuit that bypasses the air tanks
C.The engine retarder and the transmission
D.The secondary air circuit and the ABS control unit only
Explanation: The manual says the emergency brake system uses parts of the service and parking brake systems to stop the vehicle in case of a brake system failure. Spring brakes, which apply by mechanical force when air is lost, are a key part of that backup.
3On your truck, the air compressor is lubricated from its own oil supply rather than by engine oil. What pre-trip step does Maryland's CDL Manual call for?
A.Drain the compressor oil with the air tanks at the end of each day
B.Add alcohol to the compressor oil in cold weather
C.Check the compressor oil level before driving
D.Leave the compressor oil alone until the annual inspection
Explanation: The manual says the compressor may be lubricated by engine oil or have its own oil supply. If it has its own supply, check the oil level before driving.
4In an air brake system, which job belongs to the air compressor governor?
A.How much air reaches the brake chambers when you press the pedal
B.When the air compressor pumps air into the storage tanks
C.The pressure at which the spring brakes come on
D.When the safety relief valve opens
Explanation: The governor controls when the compressor pumps air into the air storage tanks. It stops pumping at the cut-out level (usually around 125 psi) and lets pumping start again at the cut-in level (usually around 100 psi).
5Tank pressure keeps rising until the governor stops the compressor from pumping. What does Maryland's CDL Manual say this cut-out level usually is?
A.About 55 psi
B.About 100 psi
C.About 125 psi
D.About 150 psi
Explanation: Section 5.1.2 says the cut-out level is usually around 125 psi. The gauge check in Section 5.3 describes building pressure to governor cut-out, usually around 120 to 140 psi, so always know your vehicle's specification.
6You have used the brakes several times and tank pressure has dropped. At about what pressure does the governor usually let the compressor start pumping again?
A.About 55 psi
B.About 85 psi
C.About 100 psi
D.About 125 psi
Explanation: That is the cut-in level, which the manual says is usually around 100 psi. Pumping then continues until pressure reaches the cut-out level, usually around 125 psi.
7According to Maryland's CDL Manual, how much air are the air storage tanks designed to hold?
A.Only enough for one full stop, so the compressor must run the whole time you drive
B.Enough to refill the drive tires if one loses pressure
C.Enough to use the brakes several times even if the compressor stops working
D.Only the air between the cut-in and cut-out levels
Explanation: The number and size of air tanks vary among vehicles, but the manual says the tanks hold enough air to allow the brakes to be used several times, even if the compressor stops working.
8Why must the air storage tanks be drained?
A.Draining the tanks is how the governor is reset to its cut-in pressure
B.Leaving air stored in the tanks overnight weakens the springs in the spring brake chambers
C.Alcohol from the evaporator collects in them and dilutes the braking force
D.Water and compressor oil collect in them, and water can freeze and cause brake failure
Explanation: Compressed air usually has some water and compressor oil in it, which are bad for the air brake system and collect in the bottom of the tanks. Water can freeze in cold weather and cause brake failure, so the manual says to drain the tanks completely at the end of each day of driving.
9A vehicle's air tanks have automatic drain valves. Which statement matches Maryland's CDL Manual?
A.They must never be opened by hand
B.They remove the need to check the alcohol evaporator every day during the winter
C.They may also allow manual draining, and some have heaters to stop freezing
D.They drain only when the engine is shut off for the night
Explanation: With automatic drains, the water and oil are drained automatically. The manual notes these tanks may be equipped for manual draining as well, and automatic drains are available with electric heating devices that help prevent freezing in cold weather.
10Your truck has an alcohol evaporator. In cold weather, how often should you check the alcohol container and fill it as needed?
A.Once a week
B.Every day
C.Only when the low air warning comes on
D.Only when the governor fails to cut out
Explanation: The alcohol evaporator puts alcohol into the air system to reduce the risk of ice in air brake valves and other parts. The manual says to check the container and fill it as needed, and in cold weather to check it every day.

About the MD CDL Air Brakes Exam

The Maryland CDL Air Brakes Knowledge Test is required by the MVA if your commercial vehicle has air brakes, including air-over-hydraulic brakes; failing or skipping it puts an L restriction on your CLP or CDL. Independent practice by OpenExamPrep covers Section 5 of the Maryland Commercial Driver's License Manual (DL-151), the four-part air brake check from Section 11, and the L and Z restriction rules. These multiple-choice questions are a study aid: they do not replace explaining and performing the air brake check in a real vehicle during the skills test.

Exam sponsor: Maryland Department of Transportation Motor Vehicle Administration (MDOT MVA). The requirements and fees below concern the certification or admission exam, separate from our free practice resources.

Assessment

A computer-based multiple-choice knowledge test at an MVA branch, in English or Spanish, taken with your other CDL knowledge tests. To drive air-braked CMVs without an L restriction, you must also take the CDL skills test in an air-brake-equipped vehicle and correctly explain and show all four parts of the air brake check (air gauge and governor cut-out, air leakage rate, air warning devices, and emergency brakes) during the Vehicle Inspection test.

Time Limit

Not published by Maryland MVA

Passing Score

80% on each CDL knowledge test

Exam / Certification Fees

No MVA fee for the knowledge test itself; the CDL learner's permit is $106 and a CDL skills retest is $20 (MVA fee table effective September 1, 2025)

Exam sponsor website

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

Official sources

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 Section 5.1 (official weight not published)

Air Brake System Parts

Compressor and governor (cut-in about 100 psi, cut-out about 125 psi), tanks and drains, alcohol evaporator, 150 psi safety valve, S-cam, wedge, and disc foundation brakes, gauges, the low air warning before 55 psi, spring brakes (20 to 45 psi), parking controls, modulating and dual parking control valves, and ABS.

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 low air warning in either system, and what happens when one half loses pressure.

Manual Section 5.3 (official weight not published)

Inspecting Air Brakes

Air brake items in the seven-step inspection: compressor belt, slack adjusters (about one inch of movement), automatic adjusters, drums, linings, hoses, ABS lamps, and the Step 7 final air brake check with its leakage and build-up limits.

Manual Section 5.4 with Section 2.16 (official weight not published)

Using Air Brakes

Normal stops, braking with ABS, controlled and stab braking, brake lag (about 32 feet at 55 mph), brake fade, the downgrade braking technique, low air pressure, and when not to use the parking brakes.

Manual Section 11.1 (official weight not published)

Maryland Skills-Test Air Brake Check

The four-part air brake check on the Vehicle Inspection test: air gauge and governor cut-out (120 to 140 psi), applied air leakage rate, low air warning devices before 55 psi, and emergency brake pop-out at 20 to 45 psi, plus the parking and service brake checks.

Manual Section 1 and MVA CDL pages (official weight not published)

Maryland CDL Rules and Restrictions

The L and Z restrictions, the Air Brakes test requirement for air-over-hydraulic vehicles, restriction removal and the 14-day CLP wait, the 80% passing score, retest waits, and CDL test languages.

Preparing for the MD CDL Air Brakes Exam

What You Need to Know

  • Passing score: 80% on each CDL knowledge test
  • Assessment: A computer-based multiple-choice knowledge test at an MVA branch, in English or Spanish, taken with your other CDL knowledge tests. To drive air-braked CMVs without an L restriction, you must also take the CDL skills test in an air-brake-equipped vehicle and correctly explain and show all four parts of the air brake check (air gauge and governor cut-out, air leakage rate, air warning devices, and emergency brakes) during the Vehicle Inspection test.
  • Time limit: Not published by Maryland MVA
  • Exam / certification fees: No MVA fee for the knowledge test itself; the CDL learner's permit is $106 and a CDL skills retest is $20 (MVA fee table effective September 1, 2025) Official sources

Using Our Practice Resources

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MD CDL Air Brakes: Suggested Study Strategy

1Use Maryland's current CDL Manual (DL-151, 05/26): the low air warning must come on before 55 psi. Older study materials that say 60 psi do not match it.
2Keep the leakage limits straight: with the brakes released, under 2 psi a minute for a single vehicle and under 3 psi for a combination; with the foot brake applied, no more than 3 psi for a single vehicle and 4 psi for a combination.
3Practice the downgrade technique from the manual: once in the proper low gear, brake just hard enough to feel a definite slowdown, release about 5 mph below your safe speed (about three seconds), and repeat.
4Rehearse saying all four parts of the Section 11 air brake check out loud; missing any part is an automatic failure of the Vehicle Inspection test.

Frequently Asked Questions

How many questions are on the Maryland CDL Air Brakes test?

The Maryland MVA does not publish a question count or time limit for the CDL Air Brakes knowledge test. The Maryland CDL Manual says you need a passing score of 80% on each CDL knowledge test.

Who needs to take the Maryland CDL Air Brakes test?

Maryland's CDL Manual says you must take the Air Brakes test if your vehicle has air brakes, including air-over-hydraulic brakes. If you fail it or don't take it, your CLP or CDL will carry an L restriction.

What is the L restriction on a Maryland CDL?

L means No Air Brake Equipped CMV. It is added if you fail or don't take the air brake knowledge test, or if you take the skills test in a vehicle without air brakes. It covers any braking system that uses air pressure fully or partially.

What is the Z restriction on a Maryland CDL?

Z means No Full Air Brake Equipped CMV. It is added if you take the skills test in a vehicle with air-over-hydraulic brakes. You may drive air-over-hydraulic vehicles but not vehicles with full air brakes.

How do I remove an air brake restriction from my Maryland CDL?

The MVA lists three steps for removing an L or Z restriction: pass the Air Brakes knowledge test; get a new commercial learner's permit and hold it for at least 14 days; and pass the pre-trip vehicle inspection and on-road skills test in an air brake equipped vehicle.

What are the four parts of the Maryland air brake check?

Section 11 of Maryland's CDL Manual lists the air gauge and governor cut-out check (about 120 to 140 psi), the air leakage rate test (no more than 3 psi a minute for a single vehicle or 4 psi for a combination, with the foot brake applied), the air warning device test (before 55 psi), and the emergency brake test (pop-out between 20 and 45 psi). Failing to explain and show all four parts is an automatic failure of the Vehicle Inspection test.

What languages is the Maryland CDL Air Brakes test offered in?

The MVA gives CDL knowledge tests on a computer in English and Spanish only, and interpreters may not assist. CDL skills tests are given only in English. This practice bank is written in English.

What happens if I fail the Maryland CDL Air Brakes test?

After a first failure, you may retest the next business day if an appointment is available. After failing two or more times, you must wait at least seven calendar days before retesting.