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200+ Free Ohio CDL Air Brakes Test Practice Questions

Pass your Ohio Commercial Driver License (CDL) Air Brakes Knowledge Test exam on the first try — instant access, no signup required.

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While driving, the low air pressure warning light comes on. What should you do?

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Key Facts: Ohio CDL Air Brakes Test Exam

80%

Minimum CDL knowledge-test passing score

49 CFR 383.135

60 psi

Low-air warning threshold

Ohio CDL Manual Section 5 / 49 CFR 393.51

20-45 psi

Typical spring-brake automatic application range

Ohio CDL Manual Section 5

150 psi

Safety valve setting

Ohio CDL Manual Section 5

12 months

Ohio CLP validity

Ohio BMV Commercial Driver - CDL

$31.50

Ohio CDL temporary permit fee

Ohio BMV Fees

Study Section 5 of the Ohio Commercial Driver License Manual. Know governor cut-in and cut-out, daily tank draining, low-air warning before 60 psi, spring-brake application around 20-45 psi, buildup and leak-test limits, ABS behavior, brake lag, safe downgrade braking, parking controls, foundation brake inspection, alcohol evaporators, and the legacy front-brake limiting valve. Ohio BMV sends applicants to driver exam stations for written tests, lists Ohio CLPs as valid for 12 months, and requires knowledge testing to remove an air-brake restriction. Federal CDL rules require at least 80% correct on knowledge tests.

Sample Ohio CDL Air Brakes Test Practice Questions

Try these sample questions to test your Ohio CDL Air Brakes Test exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 200+ question experience with AI tutoring.

1What component compresses air for the air brake system?
A.The air dryer
B.The air compressor
C.The brake chamber
D.The slack adjuster
Explanation: The air compressor pumps air into the air storage tanks. It is driven by the engine, either through belts or directly. The air dryer removes moisture from the compressed air, the brake chamber converts air pressure into mechanical force at each wheel, and the slack adjuster transfers that force to the S-cam.
2What is the typical air compressor governor cut-out pressure range?
A.60 to 80 psi
B.100 to 125 psi
C.125 to 140 psi
D.150 to 175 psi
Explanation: The governor cuts out the compressor (stops pumping) at about 125 to 140 psi. It cuts back in (resumes pumping) at about 100 to 125 psi. This pressure range keeps the system safely above the low-pressure warning threshold of 60 psi while preventing over-pressurization.
3At what pressure does the air compressor governor typically cut IN to resume pumping?
A.60 to 80 psi
B.100 to 125 psi
C.125 to 140 psi
D.145 to 150 psi
Explanation: The governor typically cuts in at 100 to 125 psi, signaling the compressor to resume pumping. It cuts out at 125 to 140 psi when system pressure is sufficient. Together these limits maintain a safe operating range well above the 60 psi low-pressure warning.
4What is the purpose of the air dryer in the brake system?
A.To cool the air before storage
B.To remove moisture and oil before air reaches the tanks
C.To increase compressed air pressure
D.To warn the driver of low pressure
Explanation: The air dryer uses a desiccant cartridge to remove water vapor and oil from compressed air before it enters the storage tanks. Removing moisture prevents corrosion, contamination of brake components, and dangerous freezing of air lines in cold weather.
5What is the function of the wet tank (supply or service reservoir)?
A.It cools brake fluid
B.It is the first storage tank where moisture collects before air moves to the other tanks
C.It supplies air only to the trailer
D.It activates the parking brakes
Explanation: The wet tank is the first storage reservoir downstream of the compressor. Most moisture and oil that gets past the air dryer settles there before clean air moves on to the primary and secondary tanks. Drivers must drain the wet tank daily to prevent contamination of the rest of the system.
6At what pressure does the safety valve in the supply tank typically open to release excess air?
A.100 psi
B.125 psi
C.150 psi
D.200 psi
Explanation: The safety valve, installed in the supply (wet) tank, is set to open at about 150 psi. It is a backup that protects the system if the governor fails to cut out the compressor. If the valve releases, the compressor or governor needs immediate repair.
7What is the role of the foot valve (also called the treadle or service brake valve)?
A.It locks the parking brake
B.It supplies air to the brake chambers in proportion to how hard the driver presses the pedal
C.It drains water from the tanks
D.It controls the trailer air supply
Explanation: The foot valve (treadle valve) meters air to the brake chambers in proportion to how far the driver depresses the brake pedal. Pressing harder sends more air, applying more braking force. Releasing the pedal exhausts air from the chambers, allowing the springs and slack adjusters to release the brakes.
8What does the brake chamber do?
A.Stores compressed air for emergencies
B.Converts air pressure into mechanical force through a pushrod
C.Cools brake drums during use
D.Acts as a backup for the parking brake
Explanation: A brake chamber is a sealed housing with a diaphragm or piston. When air pressure enters, the diaphragm pushes a pushrod outward. The pushrod rotates the slack adjuster and S-cam, which forces the brake shoes against the drum to apply braking force.
9What is the role of the slack adjuster on an S-cam brake?
A.It cushions the impact of hard braking
B.It transfers force from the pushrod to the S-cam and can be adjusted to compensate for lining wear
C.It bleeds water from the system
D.It limits maximum air pressure
Explanation: The slack adjuster is a lever that connects the brake chamber pushrod to the S-cam. As the pushrod extends, the slack adjuster rotates the S-cam, which pushes the brake shoes against the drum. It can be adjusted to maintain proper pushrod travel as brake linings wear.
10What does the S-cam do in an S-cam drum brake?
A.It releases air from the lines
B.It rotates between the brake shoes, forcing them outward against the drum
C.It cools the brake drum
D.It activates the low-pressure warning
Explanation: The S-cam is an S-shaped piece of steel between the two brake shoes. When the slack adjuster rotates it, the wide part of the S forces the shoes outward against the drum, creating friction and slowing the wheel. When air pressure is released, return springs pull the shoes back and rotate the S-cam to its original position.

About the Ohio CDL Air Brakes Test Exam

The Ohio CDL Air Brakes Knowledge Test covers the air-brake material Ohio commercial driver applicants need when operating trucks, buses, or other commercial motor vehicles equipped with air brakes or when removing an Ohio air-brake restriction. The test content follows the Ohio Commercial Driver License Manual and FMCSA CDL standards, with emphasis on compressor and governor operation, air tanks and draining, low-air warning devices, buildup and leak tests, spring and parking brakes, dual air systems, ABS, brake lag, emergency braking, slack adjusters, foundation brakes, inspection procedures, cold-weather alcohol evaporators, and older front brake limiting valves.

Assessment

Multiple-choice CDL knowledge test covering air-brake systems and Section 5 air-brake knowledge. Ohio BMV requires knowledge testing for each class, endorsement, and to remove the air-brake restriction. Federal rules require an air-brake restriction when an applicant fails the air-brake knowledge component or performs required testing in a vehicle that does not qualify for full air-brake privileges.

Time Limit

No Ohio-published Air Brakes knowledge-test time limit; Ohio publishes 30 minutes for pre-trip inspection and 40 minutes for basic maneuverability in the CDL skills test

Passing Score

At least 80% correct

Exam Fee

$31.50 CDL temporary permit; $46.50 first 4-year CDL or $92.00 first 8-year CDL; state-owned skills-test receipt is $10 pre-trip, $10 basic, and $30 road test (Ohio Bureau of Motor Vehicles (Ohio BMV))

Ohio CDL Air Brakes Test Exam Content Outline

Core Section 5 domain

Air Brake System Parts

Compressor, governor, tanks, drains, alcohol evaporator, safety valve, foot valve, foundation brakes, slack adjusters, air gauges, low-air warning, spring brakes, parking controls, ABS, and older front brake limiting valves.

Core Section 5 domain

Dual Air Brake Systems

Primary and secondary circuits, separate gauges, check valves, pressure loss, redundancy, spring brakes, parking controls, and safe response when one circuit loses pressure.

Core knowledge and skills-test domain

Inspecting Air Brakes

Governor cut-in and cut-out, air buildup rate, static and applied leak checks, low-air warning, spring-brake pop-out, parking-brake and service-brake tests, and wheel-end inspection.

Core operation domain

Using Air Brakes

Brake lag, stopping distance, normal and emergency braking, controlled and stab braking, ABS stops, brake fade, downgrade control, parking, and cold-weather moisture control.

How to Pass the Ohio CDL Air Brakes Test Exam

What You Need to Know

  • Passing score: At least 80% correct
  • Assessment: Multiple-choice CDL knowledge test covering air-brake systems and Section 5 air-brake knowledge. Ohio BMV requires knowledge testing for each class, endorsement, and to remove the air-brake restriction. Federal rules require an air-brake restriction when an applicant fails the air-brake knowledge component or performs required testing in a vehicle that does not qualify for full air-brake privileges.
  • Time limit: No Ohio-published Air Brakes knowledge-test time limit; Ohio publishes 30 minutes for pre-trip inspection and 40 minutes for basic maneuverability in the CDL skills test
  • Exam fee: $31.50 CDL temporary permit; $46.50 first 4-year CDL or $92.00 first 8-year CDL; state-owned skills-test receipt is $10 pre-trip, $10 basic, and $30 road test

Keys to Passing

  • Complete 500+ practice questions
  • Score 80%+ consistently before scheduling
  • Focus on highest-weighted sections
  • Use our AI tutor for tough concepts

Ohio CDL Air Brakes Test Study Tips from Top Performers

1Memorize the key air-brake numbers: governor cut-in/cut-out, 60 psi low-air warning, 20-45 psi spring-brake application, 150 psi safety valve, 85-to-100 psi buildup, and leak-rate limits.
2Practice the in-cab air-brake inspection sequence until you can explain each step and its pass/fail threshold.
3Separate core air-brake topics from combination-only detail unless trailer air supply, glad hands, or combination leak limits are directly relevant.
4Understand spring brakes conceptually: air holds them released, and loss of air lets the springs apply.
5Review ABS and emergency braking as control tools, not permission to drive faster or follow closer.

Frequently Asked Questions

Who administers the Ohio CDL Air Brakes test?

Ohio BMV administers CDL knowledge testing through Ohio driver exam stations and publishes the Ohio Commercial Driver License Manual used for preparation.

What score do I need to pass?

FMCSA rules require at least 80% correct on each CDL knowledge test, including the air-brake knowledge component.

Does passing the Air Brakes knowledge test remove the L restriction by itself?

Passing the knowledge test is necessary, but federal rules also tie air-brake restrictions to identifying air-brake components, conducting the air-brake systems check, and testing in a properly equipped vehicle when skills testing is required.

What Ohio CDL manual section should I study?

Study Section 5, Air Brakes. If you will pull an air-brake trailer, review combination-vehicle air-brake context too, but keep the main focus on Section 5.

How long is an Ohio CLP valid?

Ohio BMV states that a Commercial Learner Permit is valid for 12 months.

Where do I take Ohio CDL written tests?

Ohio BMV directs applicants to visit any driver exam station in Ohio for CDL written knowledge tests.