Free Oregon DMV CDL — Air Brakes Practice Test 2026
The Oregon CDL — Air Brakes knowledge test has ~25 questions, and you need ~20 correct (80%) to pass. Practice free with questions written from the official Oregon driver handbook — every one has a clear explanation, and you can retake as often as you like with no sign-up.
Content reviewed against official driver handbooks · August 12, 2026
What's on the Oregon written test
The Oregon CDL — Air Brakes knowledge test has ~25 questions; you need ~20 correct (80%) to pass.
Based on the official Oregon exam format — always confirm current details with your state DMV.
Practice by topic
Focus on one area at a time — each topic has its own set of Oregon practice questions.
How to pass the first time
- Read the official Oregon driver handbook at least once before test day.
- Practice by topic to find your weak spots, then fix them.
- Take full-length practice tests until you pass comfortably every time.
- Read every explanation — understanding beats memorizing.
Oregon CDL — Air Brakes test — frequently asked questions
How many questions are on the Oregon CDL — Air Brakes test?
The Oregon CDL — Air Brakes knowledge test has ~25 questions, and you need ~20 correct (80%) to pass. Our practice tests mirror that format.
How many questions can I miss on the Oregon CDL — Air Brakes test?
You can miss up to ~5 of the ~25 questions and still pass — you need ~20 correct, which is 80%.
Can I retake the practice test?
Yes — practice as often as you like, completely free. The questions and answer choices are shuffled each time.
Can I take the Oregon practice test in Spanish?
Yes. Every question here is available in English and Spanish — switch languages anytime. Many states also offer the real knowledge test in languages other than English; confirm what Oregon offers with your DMV.
Can I practice on my phone?
Yes. The practice tests work in any mobile or desktop browser — no app or sign-up needed — so you can study anywhere.
Are these the real DMV test questions?
No. Our questions are original, written from the current official Oregon driver handbook to match the real test's topics and style. We are not affiliated with any DMV or government agency.
What's the best way to study?
Read the Oregon driver handbook, practice by topic to target weak areas, and finish with full-length tests until you consistently pass.
Other Oregon practice tests
Take the CDL — Air Brakes test in another state
Every Oregon question is written from the official Oregon driver handbook and checked against its current edition. DMV Test Free is a free, independent study resource — not affiliated with any DMV or government agency. About DMV Test Free
Oregon CDL — Air Brakes questions with answers
20 sample questions from the Oregon CDL — Air Brakes question bank — each with the correct answer, a short explanation, and the section of the official handbook it comes from.
Show all 20 questions with answers
1. On most air-brake vehicles, a visible low-air warning must come on before tank pressure drops under:
Correct answer: 55 psi
A warning you can see is required and must appear before the tanks fall below 55 psi (or half the governor cut-out on older vehicles).
Source: Section 5.1.11 - Low Air Pressure Warning
2. During a normal stop with a manual transmission, you should press the clutch only when:
Correct answer: engine speed has dropped close to idle
Keeping the clutch out until the engine winds down near idle helps you make a smooth, controlled stop before you select your starting gear.
Source: Section 5.4.1 - Normal Stops
3. Compared with the near-instant action of hydraulic brakes, air brakes need roughly how long for pressure to reach the brakes?
Correct answer: Half a second or more
Air brakes have a built-in lag of about a half second or more because the air has to move through the lines before the brakes engage.
Source: Section 5.4.4 - Stopping Distance
4. Truck tractors with air brakes must be equipped with antilock brakes if built on or after:
Correct answer: March 1, 1997
Air-brake truck tractors made on or after March 1, 1997 are required to have ABS.
Source: Section 5.1.16 - Antilock Braking Systems (ABS)
5. To set the parking brakes on a newer air-brake vehicle, you:
Correct answer: pull the yellow diamond-shaped knob out
Newer trucks use a yellow, diamond-shaped push-pull knob; pulling it out applies the spring parking brakes and pushing it in releases them.
Source: Section 5.4.8 - Parking Brakes
6. Why can a heavily loaded vehicle take a long distance to stop once the spring brakes apply on their own?
Correct answer: The spring brakes do not act on every axle
Spring brakes are not on all axles, so a loaded vehicle stops poorly with them alone; that is why you stop earlier while foot brakes still work.
Source: Section 5.4.7 - Low Air Pressure
7. Brake linings should be replaced when they are:
Correct answer: soaked with oil or grease, or dangerously thin
Linings must not be loose, oil- or grease-soaked, or worn dangerously thin, and mechanical parts must not be broken or missing.
Source: Section 5.3.2 - Check Brake Drums, Linings, and Hoses
8. Where should you look for a trailer's ABS malfunction lamp?
Correct answer: On the left side, at a front or rear corner
Trailer ABS malfunction lamps are yellow and located on the left side, either at the front or rear corner.
Source: Section 5.1.16 - Antilock Braking Systems (ABS)
9. If the air compressor quits while you are on the road, what are the air storage tanks sized to give you?
Correct answer: Enough stored air to work the brakes several times before pressure runs low
Tank count and size differ from vehicle to vehicle, but the reservoirs are meant to keep enough compressed air on hand for a number of brake applications even after the compressor has stopped feeding them.
Source: Section 5.1.3 - Air Storage Tanks
10. Air brakes add which element to total stopping distance that hydraulic brakes do not have?
Correct answer: Brake lag distance
Total stopping distance for air brakes is perception plus reaction plus brake lag plus braking distance; brake lag is the extra factor.
Source: Section 5.4.4 - Stopping Distance
11. Front brake limiting valves were installed on some vehicles built before which year?
Correct answer: 1975
Some vehicles made before 1975 have a front brake limiting valve and a cab control; keeping it in the normal position gives full stopping power.
Source: Section 5.1.13 - Front Brake Limiting Valve
12. How do you check that the parking brake will actually hold?
Correct answer: Set it, then gently try to pull forward in a low gear
With the parking brake on, easing forward against it in a low gear confirms it can keep the vehicle in place.
Source: Section 5.3.3 - Test Parking Brake
13. If the low-air pressure warning activates while you are driving, you should:
Correct answer: stop and safely park as soon as you can
A low-air warning may mean a leak. Controlled braking only works while air remains, so stop and park while you still have foot brakes.
Source: Section 5.4.7 - Low Air Pressure
14. When you pull hard on a manual slack adjuster, roughly how much movement suggests it needs adjustment?
Correct answer: More than about one inch
If the slack adjuster moves more than roughly an inch where the push rod attaches, it likely needs adjusting.
Source: Section 5.3.2 - Check Slack Adjusters
15. On large buses, low-pressure warning devices commonly signal at about:
Correct answer: 80 to 85 psi
It is common for the low-pressure warning on large buses to activate earlier, around 80 to 85 psi.
Source: Section 5.1.11 - Low Air Pressure Warning
16. If you need steadily more application pressure just to hold the same speed on level ground, the brakes are most likely:
Correct answer: fading
Rising application pressure to keep one speed is a sign of brake fade; the driver should ease off, slow down, and shift to a lower gear.
Source: Section 5.1.10 - Application Pressure Gauge
17. For an average driver at 55 mph in good conditions, the total stopping distance with air brakes is about:
Correct answer: over 450 feet
Adding perception, reaction, brake lag, and braking distance, the total at 55 mph comes to more than 450 feet.
Source: Section 5.4.4 - Stopping Distance
18. Air-brake trucks, buses, trailers, and converter dollies must have ABS when built on or after:
Correct answer: March 1, 1998
Other air-brake vehicles, including trucks, buses, trailers, and converter dollies, are required to have ABS if built on or after March 1, 1998.
Source: Section 5.1.16 - Antilock Braking Systems (ABS)
19. Before walking away from a truck you will leave unattended, the handbook requires you to:
Correct answer: apply the parking brakes or chock the wheels
An unattended vehicle can roll away and cause harm, so you must set the parking brakes or block the wheels before leaving it.
Source: Section 5.4.8 - Parking Brakes
20. After you release the brakes during stab braking, the wheels can take how long to begin rolling again?
Correct answer: Up to one second
It can take as much as a second for the wheels to start turning; re-applying before they roll keeps the vehicle from straightening out.
Source: Section 5.4.3 - Emergency Stops