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Free Practice Questions for OR CDL Air Brakes

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Key Facts: OR CDL Air Brakes Exam

$10

Fee per commercial knowledge test attempt

Oregon DMV CDL fee schedule

80%

Minimum passing score

49 CFR 383.135

55 psi

Oregon manual low-air warning threshold

Oregon CDL Manual Section 5

20-45 psi

Spring brake emergency pop-out range

Oregon CDL Manual Section 5

Oregon DMV requires an 80% passing score on the English-only CDL Air Brakes knowledge test; it does not publish a current official item count or time limit. Drivers must also complete the applicable air-brake skills testing to avoid or remove the L restriction.

Sample OR CDL Air Brakes Practice Questions

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

1What three distinct braking systems are combined into an operational commercial motor vehicle air brake system?
A.The service brake system, the parking brake system, and the emergency brake system
B.The hydraulic brake system, the regenerative brake system, and the friction brake system
C.The engine compression brake, the exhaust retarder, and the driveline retarder
D.The primary air system, the vacuum booster system, and the auxiliary cable system
Explanation: Air brakes combine three separate systems: the service brake system (operated by the foot pedal during driving), the parking brake system (used when parked), and the emergency brake system (uses parts of service and parking brakes to stop if air fails).
2What does the engine-driven air compressor supply to an air-brake system?
A.To pump compressed air into the air storage reservoirs (tanks)
B.To cool the foundation brake drums during downhill descents
C.To circulate hydraulic fluid through the power steering rack
D.To filter carbon monoxide out of the passenger cabin ventilation system
Explanation: The air compressor is connected to the engine by gears or a V-belt and pumps air into the air storage tanks, generating the pressurized air supply required to operate the vehicle's brakes.
3How is the air compressor in a typical commercial vehicle lubricated?
A.By the engine's own internal lubrication oil supply
B.By a separate independent oil reservoir that must be drained and refilled every 500 miles
C.Air compressors are dry-lubricated with Teflon coatings and require zero oil
D.By alcohol vapor drawn from the alcohol evaporator reservoir
Explanation: Most commercial vehicle air compressors are plumbed directly into the engine's pressurized oil lubrication system. If the compressor has its own independent oil supply, the driver must check its dipstick during pre-trip.
4What is the primary function of the air compressor governor?
A.To control when the air compressor pumps air into the storage tanks by regulating cut-in and cut-out pressures
B.To govern the maximum road speed of the commercial vehicle on interstate freeways
C.To equalize tire air pressure between inside and outside dual tires
D.To prevent water and engine oil from entering the air brake lines
Explanation: The governor monitors pressure in the air tanks. It stops compressor loading at the manufacturer's cut-out setting, commonly around 125 psi, and resumes pumping at the cut-in setting, commonly around 100 psi.
5At what typical pressure should the air compressor governor cut out (stop pumping)?
A.At the manufacturer's specified cut-out pressure, commonly around 125 psi
B.At exactly 55 psi when the dashboard light illuminates
C.Between 85 and 100 psi under normal engine idle
D.At 175 psi before the safety valve opens
Explanation: The current Oregon CDL manual describes a typical governor cut-out pressure of about 125 psi. The driver must use the manufacturer's specification for the particular vehicle rather than assume a narrow universal range.
6When should the governor normally cause the air compressor to resume pumping?
A.At the manufacturer's specified cut-in pressure, commonly around 100 psi
B.At 55 psi when the warning buzzer sounds
C.At 45 psi when the spring brakes begin to drag
D.At 130 psi during continuous highway cruising
Explanation: When tank pressure drops as brakes are used, the governor causes the compressor to resume pumping at its cut-in setting. The Oregon manual describes about 100 psi as typical while directing drivers to follow the manufacturer's specification.
7What brake-system hazard is reduced by regularly draining moisture and oil from compressed-air storage tanks?
A.Water can freeze in cold weather and cause complete brake failure, and compressor oil can degrade rubber valves and diaphragms
B.Accumulated water increases the gross vehicle weight rating beyond legal highway limits
C.Moisture causes the air pressure gauge needles to stick permanently at 150 psi
D.Oil vapors react with nitrogen to produce flammable propane gas in brake lines
Explanation: Compressed air contains water vapor that condenses into liquid in storage tanks, along with traces of compressor oil. In freezing weather, water freezes in valves and lines, causing sudden brake failure. Oil destroys rubber seals.
8How often should a commercial driver drain manual air storage tank drain valves?
A.At the end of each day of driving
B.Once every 30 days during scheduled maintenance
C.Only in winter when ambient temperature falls below 32 degrees Fahrenheit
D.Once per year during the annual commercial vehicle inspection
Explanation: If the vehicle does not have automatic heated air tank drains, the driver must open all manual drain petcocks at the end of every operating day to purge accumulated moisture and sludge.
9What is the function of an alcohol evaporator installed in an air brake system?
A.To put alcohol vapor into the air system to prevent moisture from freezing in cold weather
B.To clean compressor piston rings during high-speed highway operation
C.To increase the octane rating of diesel fuel entering the injection pump
D.To cool the compressed air before it enters the foundation brake chambers
Explanation: Some air brake systems have an alcohol evaporator that introduces alcohol vapor into the air lines. Alcohol lowers the freezing point of water, preventing ice formation in valves and lines during freezing weather.
10What maintenance does an alcohol evaporator require from the driver during cold winter months?
A.Check the alcohol level daily and keep it filled with approved alcohol
B.Drain the alcohol completely before driving in freezing temperatures
C.Clean the evaporator with gasoline once per week
D.Replace the evaporator heating element every 1,000 miles
Explanation: In cold weather, the driver must check the alcohol level every day and fill it with manufacturer-approved alcohol. Daily tank draining is still required even when using an alcohol evaporator.

About the OR CDL Air Brakes Exam

The Oregon CDL Air Brakes written knowledge test is administered by Oregon DMV for commercial drivers operating vehicles equipped with air brake systems. It covers Section 5 of the Oregon Commercial Driver Manual, including the parts of an air brake system (compressor, governor, reservoirs, safety valves, brake chambers, slack adjusters), dual air brake systems, air brake inspection procedures, step-by-step air leakage checks, and safe emergency braking techniques. OpenExamPrep provides independent English-language four-option practice questions based on the official manual and FMCSA regulations. They are not an official test simulation or a substitute for hands-on commercial vehicle training.

Exam sponsor: Oregon Driver and Motor Vehicle Services (DMV). The requirements and fees below concern the certification or admission exam, separate from our free practice resources.

Assessment

An automated knowledge test administered by Oregon DMV covering Section 5 (Air Brakes) of the current Oregon Commercial Driver Manual. Passing the knowledge test and the required air-brake skills testing prevents or removes the L restriction; candidates demonstrate air-brake inspection and operation during the CDL skills test.

Time Limit

Not published

Passing Score

80%

Exam / Certification Fees

$10 per commercial knowledge test attempt; $40 Commercial Learner Permit fee; $30 replacement-license fee when removing a restriction.

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.

Core Section 5 area

Air Brake System Components

Air compressor, governor cut-in/cut-out, storage tanks, manual and automatic drain valves, alcohol evaporators, and safety relief valves.

Core Section 5 area

Brake Controls and Foundation Brakes

Brake pedal (foot valve), S-cam drum brakes, disc brakes, wedge brakes, slack adjusters, brake pushrods, and brake drums/linings.

Core Section 5 area

Dual Air Systems and Warning Devices

Primary and secondary air systems, supply and application pressure gauges, low air pressure warnings before 55 psi, and spring brake pop-out between 20-45 psi.

Core Section 5 area

Air Brake Inspection and Leakage Tests

Engine-off static leakage check, applied pressure leakage test, low pressure warning check, emergency spring brake check, and compressor build-up timing.

Core Section 5 area

Using Air Brakes and Emergency Procedures

Normal stopping, brake lag distance, controlled braking vs stab braking, steep downgrade braking (snub braking), brake fade, and parking brake use.

Preparing for the OR CDL Air Brakes Exam

What You Need to Know

  • Passing score: 80%
  • Assessment: An automated knowledge test administered by Oregon DMV covering Section 5 (Air Brakes) of the current Oregon Commercial Driver Manual. Passing the knowledge test and the required air-brake skills testing prevents or removes the L restriction; candidates demonstrate air-brake inspection and operation during the CDL skills test.
  • Time limit: Not published
  • Exam / certification fees: $10 per commercial knowledge test attempt; $40 Commercial Learner Permit fee; $30 replacement-license fee when removing a restriction. Official sources

Using Our Practice Resources

  • Work through all 220 available questions
  • Review every answer and explanation
  • Track weak areas and revisit them
  • Use our AI tutor for tough concepts

OR CDL Air Brakes: Suggested Study Strategy

1Review Section 5 (Air Brakes) of the Oregon Commercial Driver Manual thoroughly.
2Memorize the current Oregon manual values: governor cut-out about 125 psi and cut-in about 100 psi (subject to manufacturer specifications), safety valve about 150 psi, low-air warning before 55 psi, and spring brake pop-out at 20-45 psi.
3Understand the difference between controlled braking (applying brakes as hard as possible without locking wheels) and stab braking (applying brakes all the way, releasing when wheels lock, and reapplying when wheels roll).

Frequently Asked Questions

Does Oregon DMV publish the Air Brakes knowledge test question count?

No. Oregon DMV confirms an 80% minimum passing score for commercial knowledge tests but does not publish a current official item count or time limit for the Air Brakes test.

What happens if I do not take the Air Brakes test in Oregon?

If you do not pass the Air Brakes knowledge test or do not perform the skills test in an air-brake equipped commercial vehicle, Oregon DMV will place an L restriction on your CDL, restricting you to vehicles without air brakes.

At what air pressure must the low air warning activate?

The current Oregon CDL Manual requires the visible low-air warning to activate before tank pressure drops below 55 psi; large buses commonly warn at 80-85 psi.

What are the acceptable air leakage rates during an applied brake test?

After initial pressure drop, air leakage with brakes applied must not exceed 3 psi per minute for a single vehicle or 4 psi per minute for a combination vehicle.