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Iowa Air Brakes CDL Practice Test
Free Air Brakes practice questions tailored for Iowa CDL applicants. The questions follow FMCSA standards used by the Iowa Department of Transportation.
Why this matters in Iowa
Iowa DOT administers all CDL knowledge tests on touchscreen kiosks at driver license service centers. If you are pursuing the Air Brakes portion of the Iowa CDL exam, the Iowa Department of Transportation will use the same federal core questions you practice here, plus any state-specific items the Iowa Department of Transportation chooses to include.
What you will learn
The Air Brakes test is required for any vehicle equipped with a full air brake system, an air-over-hydraulic brake system, or air-actuated parking brakes. It covers system components, dual air brake systems, parking brakes, brake fade, brake adjustment, leak rates, low-air warnings, emergency brakes, the application pressure gauge, and the daily air brake pre-trip inspection sequence.
Sample questions
- Q1. Air brakes use compressed air to apply braking force. The three braking systems on most CM…
- Q2. The compressor governor controls:
- Q3. Typical compressor cut-out pressure is approximately:
- Q4. The air pressure warning signal must activate before pressure drops below:
- Q5. Spring brakes typically apply automatically when air pressure falls to approximately:
- Q6. The air brake system air loss rate (with engine off, brakes released) for a single vehicle…
- Q7. For a combination vehicle, maximum allowed air loss with brakes released is:
- Q8. When inspecting the air brake system, you should first build pressure to:
- Q9. Brake fade is most likely on:
- Q10. The proper braking technique for a long downgrade is:
- Q11. The supply line (emergency line) on a tractor-trailer is connected by the:
- Q12. The service line (control line) is connected by the:
- Q13. The trailer hand valve (trolley valve, Johnson bar) should be used:
- Q14. A dual air brake system has:
- Q15. A leaking air tank with the pressure dropping rapidly while parked indicates:
- Q16. Brake chambers convert air pressure into:
- Q17. A slack adjuster controls:
- Q18. When checking manual slack adjuster travel, the rule of thumb is the chamber pushrod shoul…
- Q19. When draining air tanks, you should:
- Q20. The alcohol evaporator (used in some systems) helps prevent:
- Q21. The parking brake control on most newer trucks is:
- Q22. Bobtail tractors (no trailer attached) require:
- Q23. When the air brake system loses all pressure, what stops the vehicle?
- Q24. The required leak-down test before driving consists of:
- Q25. Anti-lock braking systems (ABS) on tractors and trailers are intended to:
See the full Air Brakes bank →
Iowa test logistics
The Iowa Department of Transportation charges a permit fee of $25 and a license fee of $8/year. The minimum age is 18 (intrastate) / 21 (interstate). Schedule your knowledge test through the Iowa Department of Transportation once you can score above 90% on this site's practice bank.