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Free Practice Questions for Iowa CDL Air Brakes

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Key Facts: Iowa CDL Air Brakes Exam

25 questions

Iowa Air brake knowledge test length (up to 5 may be missed)

Iowa DOT CDL Testing

55 psi

Level the low air pressure warning must come on before

Iowa CDL Manual Section 5.1.11

20 to 45 psi

Air pressure range where spring brakes come fully on

Iowa CDL Manual Section 5.1.14

120 to 140 psi

Approximate governor cutout range in Iowa's air brake check

Iowa CDL Manual Section 11.1.2

Automatic failure

Result of not explaining and demonstrating all four parts of the air brake check

Iowa CDL Manual Section 11.1.2

$10

Iowa fee to remove the air brake restriction

Iowa DOT Driver's License Fees

Iowa's Air brake knowledge test has 25 questions, and you may miss up to 5. It covers Section 5 of the Iowa CDL Manual: compressor and governor, tank drains, spring brakes, dual systems, leakage and warning tests, brake lag, fade, and downgrade braking. Removing restriction L later costs $10 and needs a road test in a full-air vehicle.

Sample Iowa CDL Air Brakes Practice Questions

Try these sample questions to review concepts for the Iowa CDL Air Brakes exam. Each question includes a detailed explanation. Start the interactive quiz above for the full 204+ question experience with AI tutoring.

1Iowa DOT publishes a question count and an allowed-miss number for each CDL test. What are they for the Air Brake test?
A.20 questions, with up to 4 missed
B.30 questions, with up to 6 missed
C.25 questions, with up to 5 missed
D.50 questions, with up to 10 missed
Explanation: Iowa DOT lists the Air brake knowledge test as 25 questions with 5 allowed misses. That is the federal 80% passing standard in 49 CFR 383.135.
2What does restriction L mean on an Iowa CLP or CDL?
A.No CMV with any type of air brakes, including air over hydraulic
B.No CMV with full air brakes; air-over-hydraulic brakes are still allowed
C.No CMV with a manual transmission
D.No tractor-trailer combination
Explanation: Restriction L bars operating a CMV equipped with any type of air brakes. For the skills test and the restriction, air brakes include any braking system operating fully or partially on the air brake principle, so air-over-hydraulic systems are covered too.
3Which of these results in restriction L on an Iowa CLP or CDL?
A.Taking the skills test in a bus with air-over-hydraulic brakes
B.Taking the skills test in a truck with an automatic transmission
C.Certifying that you will drive only within Iowa
D.Failing or not taking the air brake knowledge test
Explanation: The State must put restriction L on the CLP or CDL if the applicant does not take or fails the air brake component of the knowledge test, or performs the skills test in a vehicle not equipped with air brakes.
4You pass every knowledge test, including Air Brakes, then take the skills test in a bus with air-over-hydraulic brakes. Which restriction goes on your CDL?
A.L: no air brake equipped CMV
B.Z: no full air brake equipped CMV
C.E: no manual transmission CMV
D.None, because you passed the Air Brakes knowledge test
Explanation: If an applicant performs the skills test in a vehicle with air over hydraulic brakes, the CDL is restricted from operating a CMV with any braking system operating fully on the air brake principle: restriction Z.
5An Iowa CDL holder with restriction L wants it removed. What does Iowa DOT require?
A.Only the Air Brakes knowledge test and the fee
B.The Air Brakes knowledge test, a CLP held 14 days, then a pre-trip and road test in a full-air vehicle
C.A complete new skills test, including basic control skills, but no knowledge test
D.An eight-hour air brake class at a community college
Explanation: Iowa DOT says that to remove the air brake restriction you must pass the CDL Air Brake knowledge exam and be issued and hold a CLP for at least 14 days. After the 14 days, you must pass a pre-trip inspection and an on-the-road driving test in a commercial vehicle equipped with full air brakes.
6What fee does Iowa DOT list for removing the air brake restriction from a CDL?
A.$5
B.No fee; restrictions are removed for free
C.$12, the same as a CLP
D.$10
Explanation: Iowa DOT's fee page lists $10 to remove the air brake restriction, and $10 each to remove the full air brake, manual transmission, and tractor-trailer restrictions. Removal may also require a pre-trip inspection test or a skills and driving test.
7To remove a full air brake restriction (Z), which steps does Iowa DOT list?
A.A 14-day CLP, then a pre-trip and road test in a full-air vehicle
B.Pass the Air Brakes knowledge test only
C.Pass a written knowledge test on Section 6, Combination Vehicles, only
D.Nothing; restriction Z expires after one year
Explanation: Iowa DOT says that to remove the full air brake restriction, you must be issued and hold a CLP for at least 14 days, then pass a pre-trip inspection and an on-the-road driving test in a commercial vehicle equipped with full air brakes.
8On the Iowa vehicle inspection test, what happens if you do not explain and demonstrate all four parts of the air brake check correctly?
A.You lose a few points but may continue the test
B.The examiner demonstrates the check for you
C.Automatic failure of the vehicle inspection test
D.You retake only that part later during the same appointment
Explanation: Section 11 says failure to explain and demonstrate all four parts of the air brake check correctly results in an automatic failure of the vehicle inspection test. Iowa DOT warns that the retest needs a new appointment, which could be two or three weeks out.
9Which list matches the four parts of the air brake check in Section 11 of the Iowa CDL Manual?
A.Slack adjuster pull, drum check, hose check, and lining check
B.Static leak, buildup rate, ABS lamp, and parking brake tug
C.Glad hands, tractor protection valve, trailer tug, and service stop
D.Air gauge and governor cutout, leakage, warning devices, and emergency brakes
Explanation: The four parts are: the air gauge and governor cutout check, the air leakage rate test, the air warning device test, and the emergency brake test, in which the parking brake valve should pop out. All four must be explained and demonstrated.
10In the first part of Iowa's air brake check, you build pressure to governor cutout. About what range does Section 11 give?
A.About 120 to 140 psi, or the manufacturer's level
B.About 80 to 85 psi
C.About 150 to 160 psi on most buses and trucks
D.About 55 to 60 psi
Explanation: Start the vehicle, confirm the gauges work, build pressure to governor cutout, and identify the range of activation: approximately 120 to 140 psi or the level specified by the manufacturer. Section 5 describes cut-out as around 125 psi.

About the Iowa CDL Air Brakes Exam

Iowa drivers of commercial vehicles with air brakes, including air over hydraulic, must pass the Air brake knowledge test or carry restriction L. The test covers Section 5 of the Iowa CDL Manual, and Iowa's skills test adds a four-part air brake check that is an automatic failure if missed. This independent multiple-choice practice by OpenExamPrep helps you study those topics; it is a study aid, not a copy of the official test, and it does not replace a hands-on air brake inspection.

Exam sponsor: Iowa Department of Transportation. The requirements and fees below concern the certification or admission exam, separate from our free practice resources.

Assessment

The Air brake knowledge test covers Section 5 of the Iowa CDL Manual and is required if your vehicle has air brakes, including air over hydraulic. On the skills test, you must explain and demonstrate the four-part air brake check (governor cutout, leakage, low-air warning, and emergency brake pop-out) before the pre-trip inspection; failing it is an automatic failure. Air brakes are a restriction (L or Z), not an endorsement.

Time Limit

Iowa DOT does not publish a time limit for the Air brake knowledge test

Passing Score

80% (25 questions; up to 5 missed)

Exam / Certification Fees

No separate air brake test fee listed; $10 to remove an air brake (L) or full air brake (Z) restriction; $12 CLP (Iowa DOT)

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.

Iowa CDL Manual Sections 1 and 11 & Iowa DOT

Iowa Air Brake Rules

The 25-question/5-miss test, restrictions L and Z, Iowa's removal steps and $10 fee, and the four-part air brake check that must be passed on the skills test.

Iowa CDL Manual Section 5.1

Air Brake System Parts

Compressor and governor (cut-out about 125 psi, cut-in about 100 psi), tanks and drains, alcohol evaporator, safety valve, foundation brakes, gauges, low-air warning (before 55 psi), spring brakes (20 to 45 psi), parking controls, and ABS.

Iowa CDL Manual Section 5.2

Dual Air Brake Systems

Primary and secondary systems, which axles each serves, building 100 psi in both before driving, warning thresholds, and losing pressure in one half.

Iowa CDL Manual Section 5.3

Inspecting Air Brakes

Compressor belt, slack adjusters, automatic adjusters, drums and linings, governor test, static and applied leakage limits, warning and spring brake tests, buildup rate, and parking and service brake tests.

Iowa CDL Manual Section 5.4

Using Air Brakes

Normal and emergency stops, ABS, brake lag and stopping distance, brake fade, downgrade braking technique, low air pressure, and when not to use the parking brakes.

Preparing for the Iowa CDL Air Brakes Exam

What You Need to Know

  • Passing score: 80% (25 questions; up to 5 missed)
  • Assessment: The Air brake knowledge test covers Section 5 of the Iowa CDL Manual and is required if your vehicle has air brakes, including air over hydraulic. On the skills test, you must explain and demonstrate the four-part air brake check (governor cutout, leakage, low-air warning, and emergency brake pop-out) before the pre-trip inspection; failing it is an automatic failure. Air brakes are a restriction (L or Z), not an endorsement.
  • Time limit: Iowa DOT does not publish a time limit for the Air brake knowledge test
  • Exam / certification fees: No separate air brake test fee listed; $10 to remove an air brake (L) or full air brake (Z) restriction; $12 CLP (Iowa DOT) Official sources

Using Our Practice Resources

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Iowa CDL Air Brakes: Suggested Study Strategy

1Study Section 5 of the Iowa CDL Manual, then the four-part air brake check in Section 11.
2Memorize the pressure figures: cut-in about 100 psi, cut-out about 125 psi (120 to 140 psi on the skills test), safety valve about 150 psi, low-air warning before 55 psi, spring brakes at 20 to 45 psi.
3Learn the leakage limits: static under 2 psi (single) or 3 psi (combination) per minute; applied no more than 3 psi (single) or 4 psi (combination).
4Practice the downgrade technique: brake until about 5 mph below your safe speed (about three seconds), release, and repeat.
5Know the restrictions: L for no air brakes and Z for air-over-hydraulic testing, and how Iowa removes each one.

Frequently Asked Questions

Is air brakes an endorsement in Iowa?

No. Air brakes are handled as a restriction. If you fail or skip the air brake knowledge test, or take the skills test in a vehicle without air brakes, Iowa adds restriction L; testing in an air-over-hydraulic vehicle adds restriction Z.

How many questions are on the Iowa CDL Air brake test?

Iowa DOT lists the Air brake knowledge test as 25 questions, and you may miss up to 5, which is the 80% passing standard.

How do I remove the air brake restriction from my Iowa CDL?

Iowa DOT says to pass the Air brake knowledge test, get and hold a CLP for at least 14 days, and then pass a pre-trip inspection and an on-road driving test in a vehicle with full air brakes. The fee to remove the restriction is $10.

At what pressure must the low air warning come on?

The Iowa CDL Manual says a visible warning must come on before tank pressure falls below 55 psi (or half the governor cutout pressure on older vehicles). Many large buses signal at 80 to 85 psi.

What are the air leakage limits in the air brake check?

With the brakes released (static), the loss should be under 2 psi per minute for a single vehicle and under 3 psi for a combination. With the foot brake held (applied), more than 3 psi per minute for a single vehicle or 4 psi for a combination is too much.