HI · L (restriction removed) Endorsement

Hawaii Air Brakes CDL Practice Test

Below are 25 exam-style questions for the Hawaii Air Brakes CDL knowledge test, modeled on the FMCSA-aligned content used by the Hawaii Department of Transportation. Try to answer each question on your own before reading the answer key directly under it. The questions and answer choices are shuffled deterministically per state and endorsement, so the order will stay the same on repeat visits — that lets you genuinely measure your improvement.

Heads up: this is a study tool, not a graded exam. Cover the answer with your hand or a sheet of paper for an honest practice run, then re-read the explanations for any questions you missed. Aim for 22 out of 25 or better, three times in a row, before scheduling the real exam.

Question 1 of 25

Why should you NOT use the trailer hand valve to hold a parked combination vehicle?

A It will activate the spring brakes
B It is illegal
C Air leaks could cause the brakes to release and let the vehicle roll
D It only works while the engine is running

Correct answer: C

The hand valve relies on continuous air pressure. A slow leak releases the brakes and the vehicle rolls.

Question 2 of 25

Slack adjusters should be checked because:

A They affect engine performance
B They control trailer height
C Out-of-adjustment slack adjusters can result in brakes that do not work properly
D They are decorative

Correct answer: C

Slack adjusters convert pushrod motion into braking force. Out-of-adjustment slack adjusters reduce braking ability and are a common out-of-service item.

Question 3 of 25

A driver should never:

A Test the parking brake
B Make pre-trip inspections
C Drain the wet tank
D Use the trailer hand valve as a parking brake

Correct answer: D

The trailer hand valve is not a parking device — see the trailer-hand-valve question. Always set the trailer parking brakes.

Question 4 of 25

You should test the parking brake by:

A Pressing the service brake while parked
B Setting the parking brake, releasing the service brake, and gently trying to move the vehicle
C Driving over a curb
D Doing nothing — the dashboard light is enough

Correct answer: B

Apply throttle gently in low gear; if the truck moves, the parking brake is not holding.

Question 5 of 25

A brake check ahead of a downgrade should be done:

A Once a year
B Before reaching the top, while still on level ground
C At the bottom only
D In the middle of the descent

Correct answer: B

A brief brake test on level ground at the top reveals problems while you can still stop safely.

Question 6 of 25

After parking a tractor-trailer:

A Set only the tractor parking brake
B Leave both released
C Set only the trailer parking brake
D Set both tractor and trailer parking brakes

Correct answer: D

Federal practice is to set both parking brakes when fully parked. The exception is during coupling/uncoupling, where the trailer brakes are set.

Question 7 of 25

When applying brakes in an emergency without ABS:

A Pump rapidly and lightly
B Use stab braking — apply hard, release when wheels lock, re-apply
C Press as hard as possible and hold
D Use only the parking brake

Correct answer: B

Stab braking keeps the truck straight in an emergency without ABS. Hard continuous pressure can lock the wheels and cause a jackknife.

Question 8 of 25

On a vehicle with dual air brakes, the warning device must come on before pressure in either system drops below:

A 40 psi
B Never; only the gauge needs to read it
C 60 psi
D 20 psi

Correct answer: C

The low-air warning must activate before pressure drops below 60 psi in either circuit.

Question 9 of 25

In a dual system, normal cut-in pressure is approximately:

A 40 psi
B 60 psi
C 125 psi
D 85 psi

Correct answer: B

Cut-in is usually around 100 psi but cut-out is around 125 psi. Cut-in below 60 psi indicates a problem in many systems.

Question 10 of 25

When applying the foot brake hard:

A Air pressure should remain unchanged
B The compressor cuts out
C Air pressure may drop slightly
D Air pressure increases

Correct answer: C

A small drop is expected during heavy application. The compressor recharges the system back up to cut-out pressure.

Question 11 of 25

You should not over-tighten a glad-hand because:

A It is bad luck
B It violates federal weight law
C It can damage the rubber seals
D It will reduce engine power

Correct answer: C

Over-tightening crushes the seals. The connection should be firm but not forced.

Question 12 of 25

A correctly adjusted brake will have:

A No slack adjuster
B Loose drum bolts
C Pushrod travel within the legal limit for that brake type
D Visible rust

Correct answer: C

Pushrod travel must be within the manufacturer's and federal limits — exact value depends on chamber size.

Question 13 of 25

A dual air-brake system means:

A Two governors
B Two separate air-brake systems on one set of brake controls
C Two compressors
D Twice the air pressure

Correct answer: B

Modern trucks have two separate air systems (often labeled primary and secondary) with one set of brake controls so a failure in one circuit still leaves working brakes.

Question 14 of 25

A common cause of an air-brake skid is:

A Locking the wheels by braking too hard
B Both of the above
C Neither of the above
D Driving too fast for conditions

Correct answer: B

Skids result when the wheel locks and the tire loses traction. Speed and over-application are both common contributors.

Question 15 of 25

When approaching a long downgrade, you should:

A Skip the brake test
B Coast in neutral
C Test the brakes at the bottom
D Test the brakes by lightly applying them at the top

Correct answer: D

A light brake application at the top tests for pulling or weakness before the descent puts heat into the system.

Question 16 of 25

When you press the brake pedal, brake pressure is:

A Released from the storage tanks
B Built up from zero by the pedal
C Created by the pedal mechanically
D Received from a separate accumulator

Correct answer: A

Pressing the pedal releases stored air from the tanks into the brake chambers; the pedal does not generate pressure itself.

Question 17 of 25

The proper braking technique on a long downgrade is:

A Coast in neutral
B Apply the parking brake
C Light, intermittent braking with engine braking and a low gear
D Heavy continuous braking

Correct answer: C

Use the proper low gear so engine braking does most of the work; brief, moderate brake applications keep the speed in check.

Question 18 of 25

In a combination vehicle, with the brakes applied and the engine off, the maximum allowable air loss is:

A 3 psi per minute
B 5 psi per minute
C 2 psi per minute
D 4 psi per minute

Correct answer: D

Combination vehicle, brakes applied: 4 psi per minute. Single vehicle, brakes applied: 3 psi per minute.

Question 19 of 25

Which is true about air storage tanks?

A They never need to be drained
B They must be drained daily to remove water and oil
C They drain themselves automatically in all trucks
D They must be drained completely once a year

Correct answer: B

Most trucks require manual daily draining of each tank. Some have automatic moisture ejectors, but the driver is still responsible.

Question 20 of 25

Anti-lock braking systems (ABS) on air-brake vehicles:

A Replace foundation brakes
B Are optional and rarely installed
C Help prevent wheel lockup but do not necessarily shorten stopping distance
D Are required only on hazmat trailers

Correct answer: C

ABS helps the driver maintain steering control by preventing wheel lockup. It does not necessarily reduce stopping distance.

Question 21 of 25

Spring brakes do NOT replace:

A The service brakes for normal stops
B The headlights
C The tail lights
D The horn

Correct answer: A

Spring brakes are for parking and emergency only — never for normal service braking.

Question 22 of 25

Brake drums in good condition will:

A Have small cracks
B Be glowing red after stops
C Be coated with oil
D Be free of cracks longer than half the width of the friction area

Correct answer: D

Cracks longer than half the friction area or any visible heat checks usually fail inspection.

Question 23 of 25

Spring-brake pop-out occurs at approximately:

A 90 to 100 psi
B 60 to 80 psi
C 0 to 10 psi
D 20 to 45 psi

Correct answer: D

Pop-out is typically between 20 and 45 psi, varying by manufacturer.

Question 24 of 25

Modulating valves on the rear axle help prevent:

A Wheel lockup during emergency braking
B Tire blowouts
C Engine overheating
D Steering wander

Correct answer: A

Modulating valves and ABS sensors release pressure briefly to keep wheels from locking.

Question 25 of 25

You should NOT drain the wet tank when:

A There is no situation in which draining is wrong
B You are about to begin a trip
C It is full of moisture
D The vehicle is in motion

Correct answer: A

Daily draining is a routine task; there is no situation where draining is unsafe (other than while driving).

Study tips for the Hawaii Air Brakes exam

The Air Brakes portion of the Hawaii CDL exam is graded out of the bank of questions the Hawaii Department of Transportation draws from each year. While the exact bank is not published, every question is sourced from the Air Brakes chapter of the Hawaii CDL handbook, which itself is derived from the FMCSA Model Commercial Driver's License Manual. That means studying our practice tests, reading the corresponding handbook chapter, and re-reading the parts you got wrong is genuinely the most efficient route to a first-time pass.

Most successful applicants follow a simple cycle: take the practice test cold, write down every question you missed, open the matching chapter of the official Hawaii handbook, re-read the section that contains the right answer, then re-take the practice test 24 to 48 hours later. The 24-hour delay matters — sleep is when your brain commits new information to long-term memory, and CDL knowledge questions reward that kind of consolidated learning rather than cramming.

Pay particular attention to questions that include qualifier words like always, never, only, primary, or most. CDL test writers love to flip the right answer with a single qualifier. When two answer choices look almost identical, pay attention to the verb (is it must, should, or may?) and to any numbers (14 days, 100 air miles, 8 hours, 70/8 split). On endorsement tests in particular, watch for trick framing where a true statement about a different endorsement is offered as the "correct" answer to a question that is actually about Air Brakes.

Test-day logistics matter too. Bring photo ID, your Social Security card or birth certificate, your medical examiner's certificate (DOT card), and proof of state residency if you haven't already submitted those documents. The Hawaii Department of Transportation will not let you sit for the knowledge exam without your documentation, and most offices charge an additional fee for re-attempts. Arrive early — the wait at most CDL testing offices runs 30 to 60 minutes — and silence your phone before the exam begins.

Finally, keep your General Knowledge fundamentals sharp even when you're focused on the Air Brakes exam. Many states administer multiple knowledge tests in a single sitting, and questions on weight definitions (GVWR, GCWR, GAWR), stopping distance, and the pre-trip inspection routine show up across endorsements. If you're unsure on the basics, sit a fresh Hawaii General Knowledge practice test before scheduling the real exam.

Next steps

Missed more than four questions? Re-read the Air Brakes study guide and the matching chapter in the official Hawaii CDL handbook. Then come back and re-take the test. Once you can score 22 of 25 or higher on three runs in a row, you're in good shape to schedule the real exam at your local Hawaii Department of Transportation office.

Already comfortable with this endorsement? Drill another: HI General Knowledge · HI Combination Vehicles · HI Hazardous Materials · HI Passenger · HI School Bus · HI Tank Vehicle · HI Doubles / Triples

New to the CDL process in Hawaii? Read How to apply for a CDL in Hawaii for the document checklist and step-by-step timeline.