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Ohio air brakes practice

Selected knowledge practice, not a complete licensing course or practical training.

Ohio CDL Air Brakes

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Question 1 of 64
  1. 1. What supplies compressed air to the brake reservoirs while the engine is running?
  2. 2. The air pressure reaches the compressor governor’s cut-out setting. What should happen?
  3. 3. Your compressor has its own oil supply rather than sharing engine lubrication. What additional maintenance check is needed?
  4. 4. Why can an air-braked vehicle still have several brake applications available after the compressor stops pumping?
  5. 5. Why is water left in an air-brake reservoir especially dangerous in freezing weather?
  6. 6. Your vehicle has manual air-tank drains. What does the Ohio CDL handbook advise?
  7. 7. A truck has an alcohol evaporator for its air system. How should it be treated?
  8. 8. The air reservoir’s safety relief valve opens because system pressure is too high. What does this indicate?
  9. 9. In normal air-brake operation, pressing the brake pedal farther generally does what?
  10. 10. When you release the air-brake pedal after a normal application, what happens to the air used for that application?
  11. 11. Why should you avoid pumping air brakes unnecessarily?
  12. 12. What actually slows the wheel when a drum-type service brake applies?
  13. 13. In an S-cam drum brake, what does rotation of the S-cam do?
  14. 14. What does a supply air-pressure gauge tell the driver?
  15. 15. On a vehicle fitted with an application-pressure gauge, more pressure than usual is needed to maintain the same speed downhill. What may this suggest?
  16. 16. How are the stop lights commonly activated in the air-brake system described by the handbook?
  17. 17. In a spring-brake chamber, what normally holds the powerful parking spring back so the brake can release?
  18. 18. Why can poor brake adjustment weaken both service braking and spring-brake holding on the same wheel?
  19. 19. On a vehicle with the standard yellow diamond-shaped parking-brake control, how do you apply the parking brakes?
  20. 20. Why should you avoid a strong service-brake application while spring brakes are applied on a vehicle without anti-compounding protection?
  21. 21. A bus is equipped with a modulating valve for spring brakes. What is that control designed to permit?
  22. 22. Some buses have a separate reserve that can release the spring brakes in an emergency. What limitation matters?
  23. 23. An older vehicle has a driver-operated front-brake limiting valve marked NORMAL and SLIPPERY. For normal stopping, which setting does the handbook specify?
  24. 24. What makes a dual air-brake system different from one single air circuit?
  25. 25. Before moving a vehicle with two service-air circuits, what should you check on the pressure gauges?
  26. 26. One circuit in a dual air-brake system loses pressure during a trip. Why is continuing the trip unsafe?
  27. 27. What should be inspected when the air compressor is belt-driven?
  28. 28. An automatic slack adjuster repeatedly needs manual readjustment. What is the sound response?
  29. 29. Is one inch the universal legal maximum applied pushrod stroke for every commercial-vehicle brake chamber?
  30. 30. During inspection, you find oil or grease on a brake lining. How should you regard it?
  31. 31. An air hose is rubbing against a sharp metal edge. What should you recognize?
  32. 32. Before releasing parking brakes for the handbook’s stationary applied-air-leak test, what is essential?
  33. 33. For the handbook’s applied-air-leak check, when does the one-minute measurement begin?
  34. 34. A single vehicle loses 4 psi in one minute after the full applied-brake pressure has stabilized, with the engine off and the test properly set up. How does this compare with the Ohio CDL handbook limit?
  35. 35. In the Ohio CDL handbook’s applied-leak check for a truck-and-one-trailer combination, pressure falls 5 psi in one minute after stabilizing. What does that mean?
  36. 36. Why does the handbook’s engine-off low-air warning test keep the electrical power on?
  37. 37. The low-air warning comes on while you are driving. What should you do before pressure falls farther?
  38. 38. Why must a driver use the manufacturer’s specified pressure range when checking automatic spring-brake application?
  39. 39. For the ordinary dual-air-system example in the Ohio CDL handbook, what buildup check is described at operating rpm?
  40. 40. After building air pressure and following the safe test setup, how does the handbook check that the parking brake holds?
  41. 41. During a safe, low-speed service-brake check, the vehicle pulls to one side and the response feels delayed. What should you conclude?
  42. 42. What extra part of stopping distance must an air-brake driver allow for, beyond perception, reaction and wheel-braking distance?
  43. 43. The handbook warns against applying parking brakes when they are very hot. What must a driver still ensure while following the cooling procedure?
  44. 44. Under the cited current FMVSS 121 requirement, ignition is in RUN and service-reservoir pressure is below 60 psi. What must the warning signal do?
  45. 45. For a non-exempt air-braked power unit not subject to FMVSS 121 when manufactured, the governor cuts out at 100 psi. Under 49 CFR 393.51(c)(2), at what pressure and below is continuous warning required?
  46. 46. Under the cited FMVSS 121 gauge requirement, what pressure information must be readily visible from the normal driving position?
  47. 47. Under federal commercial-vehicle brake equipment rules, how must corresponding brake chambers on the two ends of an axle compare?
  48. 48. Which minimum thickness must commercial-vehicle brake drums and rotors meet under 49 CFR 393.47(g)?
  49. 49. What does ABS do when a braked wheel is about to lock?
  50. 50. The yellow ABS malfunction lamp stays on after its normal startup check. What should you suspect?
  51. 51. Does ABS guarantee a shorter stop in every road condition?
  52. 52. A straight truck has working ABS on every axle. In an emergency requiring maximum braking, what does the Ohio manual permit?
  53. 53. On a long downgrade, how should service braking relate to engine braking in the Ohio handbook's method?
  54. 54. In the handbook's downgrade example, your selected safe speed is 40 mph. After applying the brakes for a definite slowdown, at about what speed do you release them?
  55. 55. How can repeated heavy service-brake use on a descent reduce braking effectiveness?
  56. 56. Several brakes are out of adjustment during a descent. What can happen to the brakes still doing their share?
  57. 57. In Section 5's stationary released-brake leakage check, a properly secured single vehicle loses 3 psi in one minute. How does that compare with the handbook's criterion?
  58. 58. Why must you identify which leakage test is being performed before judging the pressure drop?
  59. 59. Which sequence matches Ohio's Section 11 air-brake inspection demonstration?
  60. 60. For the air-brake portion of Ohio's vehicle-inspection test, is naming the four checks enough?
  61. 61. During the emergency-brake check, the vehicle's valves are not designed to pop out. What indication does Ohio's manual tell you to identify?
  62. 62. Under Ohio's Section 11 check for an air-operated trailer, when should its tractor-protection and trailer parking/emergency valves close relative to the power-unit valve?
  63. 63. What must you explain about valve pop-out in the primary/secondary air system described by Ohio's Section 11?
  64. 64. After switching off the engine for Ohio's Section 11 applied-leakage check, which key position is specified?
Review all 64 questions with answers

  1. What supplies compressed air to the brake reservoirs while the engine is running?

    Correct answer: The air compressor.

    The compressor pumps air into the reservoirs. The other components transmit braking force or hold the brakes, rather than replenish stored air.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Air compressor; physical PDF page 69 (printed 5-1); reviewed September 14, 2026. ↗

  2. The air pressure reaches the compressor governor’s cut-out setting. What should happen?

    Correct answer: The compressor stops pumping air into the system.

    The governor controls pumping at the cut-in and cut-out settings. Cut-out does not mean the engine stops or the reservoirs are emptied; use the vehicle’s specified pressure settings.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Governor cut-out; physical PDF page 69 (printed 5-1); reviewed September 14, 2026. ↗

  3. Your compressor has its own oil supply rather than sharing engine lubrication. What additional maintenance check is needed?

    Correct answer: Check that compressor’s oil level.

    Some compressors have a separate oil supply. An acceptable engine oil level does not establish that a separately lubricated compressor has enough oil.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Separate compressor lubrication; physical PDF page 69 (printed 5-1); reviewed September 14, 2026. ↗

  4. Why can an air-braked vehicle still have several brake applications available after the compressor stops pumping?

    Correct answer: The reservoirs hold a supply of compressed air.

    Reservoirs store braking air. That reserve is limited: it does not make continued driving with a failed air supply safe.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Stored-air reserve; physical PDF page 69 (printed 5-1); reviewed September 14, 2026. ↗

  5. Why is water left in an air-brake reservoir especially dangerous in freezing weather?

    Correct answer: It can freeze and interfere with brake operation.

    Moisture can freeze in the system and cause brake trouble. The handbook calls for draining water and oil from tanks using the equipment’s proper procedure.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Water in air tanks; physical PDF page 69 (printed 5-1); reviewed September 14, 2026. ↗

  6. Your vehicle has manual air-tank drains. What does the Ohio CDL handbook advise?

    Correct answer: Drain the tanks at the end of each working day.

    Manual drains remove collected water and oil. Waiting for a malfunction allows contamination to build up; follow the vehicle’s drain procedure and maintenance instructions.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Manual reservoir drains; physical PDF page 69 (printed 5-1); reviewed September 14, 2026. ↗

  7. A truck has an alcohol evaporator for its air system. How should it be treated?

    Correct answer: Maintain it as specified; it does not eliminate tank-drain checks.

    An alcohol evaporator is fitted only on some systems. Follow the equipment’s instructions and continue required moisture-management checks; do not improvise additives for other systems.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Alcohol evaporator equipment; physical PDF page 69 (printed 5-1); reviewed September 14, 2026. ↗

  8. The air reservoir’s safety relief valve opens because system pressure is too high. What does this indicate?

    Correct answer: A system problem needs attention by a mechanic.

    The safety valve protects against excessive pressure. Its operation is a reason to find the fault, not disable the protection or assume the brakes are otherwise sound.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Safety valve discharge; physical PDF page 70 (printed 5-2); reviewed September 14, 2026. ↗

  9. In normal air-brake operation, pressing the brake pedal farther generally does what?

    Correct answer: Applies more air pressure to the service brakes.

    The foot valve meters service-brake pressure according to pedal demand. It does not adjust the governor’s pressure setting.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Foot valve pressure; physical PDF page 70 (printed 5-2); reviewed September 14, 2026. ↗

  10. When you release the air-brake pedal after a normal application, what happens to the air used for that application?

    Correct answer: It is exhausted from the brake chambers.

    Releasing the pedal vents the application air so the service brakes can release. New air must be supplied from the reservoirs for later applications.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Releasing the service pedal; physical PDF page 70 (printed 5-2); reviewed September 14, 2026. ↗

  11. Why should you avoid pumping air brakes unnecessarily?

    Correct answer: Repeated applications can use air faster than it is replenished.

    Each application consumes air. Repeated unnecessary applications can reduce the available reserve, especially if the compressor cannot keep up.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Repeated unnecessary pumping; physical PDF page 70 (printed 5-2); reviewed September 14, 2026. ↗

  12. What actually slows the wheel when a drum-type service brake applies?

    Correct answer: Friction between the brake lining and the drum.

    Air pressure operates the brake mechanism, but contact between lining and drum creates the friction that slows the wheel and produces heat.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Drum brake friction; physical PDF page 70 (printed 5-2); reviewed September 14, 2026. ↗

  13. In an S-cam drum brake, what does rotation of the S-cam do?

    Correct answer: Pushes the brake shoes outward against the drum.

    The chamber’s pushrod and slack adjuster turn the camshaft. The S-shaped cam spreads the shoes against the inside of the drum. This describes S-cam brakes, not every air-brake design.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): S-cam action; physical PDF page 70 (printed 5-2); reviewed September 14, 2026. ↗

  14. What does a supply air-pressure gauge tell the driver?

    Correct answer: How much air pressure is available in the reservoir system.

    Supply gauges monitor stored air pressure. They do not measure lining wear or show the individual braking force at each wheel.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Supply pressure reading; physical PDF page 70 (printed 5-2); reviewed September 14, 2026. ↗

  15. On a vehicle fitted with an application-pressure gauge, more pressure than usual is needed to maintain the same speed downhill. What may this suggest?

    Correct answer: Brake fade or another braking-system problem.

    An unusual increase in required application pressure can indicate fade, adjustment trouble, leaks or other mechanical problems. The gauge alone does not identify the exact fault.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Application pressure trend; physical PDF page 70 (printed 5-2); reviewed September 14, 2026. ↗

  16. How are the stop lights commonly activated in the air-brake system described by the handbook?

    Correct answer: Air pressure operates an electrical switch.

    An air-operated electrical switch turns on the stop lights when the service brakes are applied. The warning system and parking control serve different purposes.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Brake-light switch; physical PDF page 70 (printed 5-2); reviewed September 14, 2026. ↗

  17. In a spring-brake chamber, what normally holds the powerful parking spring back so the brake can release?

    Correct answer: Air pressure.

    Air holds the parking spring compressed. When that holding pressure is released or lost, the spring can apply the brake; this differs from service brakes that use air to apply.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Spring-brake release; physical PDF page 71 (printed 5-3); reviewed September 14, 2026. ↗

  18. Why can poor brake adjustment weaken both service braking and spring-brake holding on the same wheel?

    Correct answer: Both rely on properly adjusted foundation-brake components.

    The spring brake and service brake depend on the wheel’s brake mechanism. A spring application does not overcome improper foundation-brake adjustment.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Shared adjustment consequences; physical PDF page 71 (printed 5-3); reviewed September 14, 2026. ↗

  19. On a vehicle with the standard yellow diamond-shaped parking-brake control, how do you apply the parking brakes?

    Correct answer: Pull the control out.

    The standard yellow diamond control is pulled to apply and pushed to release. Older or special equipment may use a different control, so know the vehicle before operation.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Parking control direction; physical PDF page 71 (printed 5-3); reviewed September 14, 2026. ↗

  20. Why should you avoid a strong service-brake application while spring brakes are applied on a vehicle without anti-compounding protection?

    Correct answer: The combined forces can damage brake components.

    Service and spring forces can add together at the brake mechanism. Some vehicles have protection, but the driver must not assume every vehicle does.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Brake compounding; physical PDF page 71 (printed 5-3); reviewed September 14, 2026. ↗

  21. A bus is equipped with a modulating valve for spring brakes. What is that control designed to permit?

    Correct answer: Gradual control of spring-brake application.

    A modulating control can vary spring-brake application rather than providing only an on/off action. Operation and securing the control for parking depend on the vehicle’s instructions.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Modulating parking control; physical PDF page 71 (printed 5-3); reviewed September 14, 2026. ↗

  22. Some buses have a separate reserve that can release the spring brakes in an emergency. What limitation matters?

    Correct answer: The reserve permits only a limited number of releases.

    An emergency-release reserve is finite and vehicle-specific. Its presence is not permission to continue passenger service with an unsafe braking system.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Emergency release reserve; physical PDF page 71 (printed 5-3); reviewed September 14, 2026. ↗

  23. An older vehicle has a driver-operated front-brake limiting valve marked NORMAL and SLIPPERY. For normal stopping, which setting does the handbook specify?

    Correct answer: NORMAL.

    The handbook specifies NORMAL to preserve normal stopping power. This question concerns the older manually controlled limiter, not ABS or a modern automatic system.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Older front-brake limiter; physical PDF page 71 (printed 5-3); reviewed September 14, 2026. ↗

  24. What makes a dual air-brake system different from one single air circuit?

    Correct answer: It has two air systems with separate reservoirs and lines.

    Dual systems have separate air circuits operated through a common brake control. The exact axle arrangement depends on the vehicle.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Dual-system separation; physical PDF page 73 (printed 5-5); reviewed September 14, 2026. ↗

  25. Before moving a vehicle with two service-air circuits, what should you check on the pressure gauges?

    Correct answer: That both circuits have reached the required operating pressure.

    The handbook says to allow both systems to build adequate pressure. One satisfactory reading does not establish that the other circuit is ready; follow the vehicle’s specified procedure.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Checking both circuits; physical PDF page 73 (printed 5-5); reviewed September 14, 2026. ↗

  26. One circuit in a dual air-brake system loses pressure during a trip. Why is continuing the trip unsafe?

    Correct answer: Some braking may be lost and stopping distance can increase.

    A surviving circuit provides limited protection during failure, not normal service capability. Stop safely and have the problem corrected.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): One circuit loses pressure; physical PDF page 73 (printed 5-5); reviewed September 14, 2026. ↗

  27. What should be inspected when the air compressor is belt-driven?

    Correct answer: The belt’s condition and proper tension.

    A worn, damaged or improperly tensioned drive belt can affect compressor operation. This check applies when the compressor uses a belt, not a gear drive.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Belt-driven compressor inspection; physical PDF page 73 (printed 5-5); reviewed September 14, 2026. ↗

  28. An automatic slack adjuster repeatedly needs manual readjustment. What is the sound response?

    Correct answer: Have a qualified person find and repair the underlying fault.

    Repeated manual readjustment can hide a problem in the adjuster, installation or foundation brake. It does not replace diagnosis and proper repair.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Automatic slack-adjuster fault; physical PDF page 74 (printed 5-6); reviewed September 14, 2026. ↗

  29. Is one inch the universal legal maximum applied pushrod stroke for every commercial-vehicle brake chamber?

    Correct answer: No; use the limit for the actual actuator type and size.

    Federal limits depend on the actuator. The handbook’s approximate manual free-play check must not be confused with a universal applied-stroke limit. Unlisted actuator types have the manufacturer-related limits specified by the rule.

    Source: 49 CFR 393.47(e)(1)–(2); actuator-specific principle only, no table value reproduced. Official eCFR XML dated September 10, 2026; reviewed September 14, 2026. ↗

  30. During inspection, you find oil or grease on a brake lining. How should you regard it?

    Correct answer: As a brake defect that needs attention before safe operation.

    Brake linings rely on controlled friction. Oil or grease contamination is an unsafe condition, not a desirable lubricant for the friction surface.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Contaminated brake lining; physical PDF page 74 (printed 5-6); reviewed September 14, 2026. ↗

  31. An air hose is rubbing against a sharp metal edge. What should you recognize?

    Correct answer: The rubbing can damage the hose and cause air loss.

    Inspect hoses for cuts, rubbing and damage. A warning device can alert the driver to pressure loss but cannot prevent a damaged hose from leaking.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Damaged air hose; physical PDF page 74 (printed 5-6); reviewed September 14, 2026. ↗

  32. Before releasing parking brakes for the handbook’s stationary applied-air-leak test, what is essential?

    Correct answer: Secure the vehicle against rolling, including proper wheel chocks.

    Some air-system checks require releasing the parking brakes. Establish proper rollaway protection first and follow the vehicle’s full inspection procedure.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Applied-leak test preparation; physical PDF page 74 (printed 5-6); reviewed September 14, 2026. ↗

  33. For the handbook’s applied-air-leak check, when does the one-minute measurement begin?

    Correct answer: After a full brake application and the initial gauge drop has stabilized.

    The initial air used to apply the brakes is different from continued leakage. Hold the application and measure the drop for one minute after the initial change settles.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Applied-leak timing; physical PDF page 74 (printed 5-6); reviewed September 14, 2026. ↗

  34. A single vehicle loses 4 psi in one minute after the full applied-brake pressure has stabilized, with the engine off and the test properly set up. How does this compare with the Ohio CDL handbook limit?

    Correct answer: It exceeds the 3-psi-per-minute single-vehicle limit.

    For this applied check, the handbook gives no more than 3 psi in one minute for a single vehicle. A 4-psi loss exceeds that criterion and requires correction before driving.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Single-vehicle applied leakage; physical PDF page 74 (printed 5-6); reviewed September 14, 2026. ↗

  35. In the Ohio CDL handbook’s applied-leak check for a truck-and-one-trailer combination, pressure falls 5 psi in one minute after stabilizing. What does that mean?

    Correct answer: It exceeds the stated 4-psi-per-minute combination limit.

    The handbook’s combination-vehicle criterion is no more than 4 psi in one minute during the applied test. This question does not assign that limit to every possible multi-trailer configuration.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Combination applied leakage; physical PDF page 74 (printed 5-6); reviewed September 14, 2026. ↗

  36. Why does the handbook’s engine-off low-air warning test keep the electrical power on?

    Correct answer: So the electrical warning devices can operate as pressure is reduced.

    The warning test requires electrical power for the warning circuit. The engine is off while pressure is reduced according to the safe inspection procedure.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Warning test electrical supply; physical PDF page 74 (printed 5-6); reviewed September 14, 2026. ↗

  37. The low-air warning comes on while you are driving. What should you do before pressure falls farther?

    Correct answer: Make a safe stop and secure the vehicle as soon as possible.

    Act while you still have enough air to control the stop. Waiting for an automatic spring-brake application can leave much less control and may not apply every axle.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Low-air warning response; physical PDF page 77 (printed 5-9); reviewed September 14, 2026. ↗

  38. Why must a driver use the manufacturer’s specified pressure range when checking automatic spring-brake application?

    Correct answer: The application pressure varies with the brake equipment.

    The handbook gives a typical range, not one exact pressure for all systems. The brakes may apply with air still in the tanks; use the specified procedure and limits.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Automatic application pressure; physical PDF page 75 (printed 5-7); reviewed September 14, 2026. ↗

  39. For the ordinary dual-air-system example in the Ohio CDL handbook, what buildup check is described at operating rpm?

    Correct answer: 85 to 100 psi within 45 seconds, with larger-reservoir exceptions.

    The handbook describes the 85-to-100-psi, 45-second check and says unusually large reservoirs may take longer. Follow manufacturer specifications; this is not a universal federal vehicle-design test limit.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Handbook pressure-buildup check; physical PDF page 75 (printed 5-7); reviewed September 14, 2026. ↗

  40. After building air pressure and following the safe test setup, how does the handbook check that the parking brake holds?

    Correct answer: Gently try to pull against the applied parking brake in a low gear.

    The handbook uses a gentle low-gear pull against the applied parking brake. Use a safe area and the vehicle’s procedure; a control’s appearance does not prove holding ability.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Parking-brake holding check; physical PDF page 75 (printed 5-7); reviewed September 14, 2026. ↗

  41. During a safe, low-speed service-brake check, the vehicle pulls to one side and the response feels delayed. What should you conclude?

    Correct answer: A braking problem needs investigation and correction.

    Pulling, delayed response or unusual feel can reveal trouble. The check identifies a symptom, not one certain component failure.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Service-brake inspection result; physical PDF page 75 (printed 5-7); reviewed September 14, 2026. ↗

  42. What extra part of stopping distance must an air-brake driver allow for, beyond perception, reaction and wheel-braking distance?

    Correct answer: Distance traveled while the air brakes respond to the application.

    Air pressure takes time to reach and operate the brakes. The distance traveled during that delay adds to stopping distance and varies with speed and conditions.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Air-brake lag; physical PDF page 76 (printed 5-8); reviewed September 14, 2026. ↗

  43. The handbook warns against applying parking brakes when they are very hot. What must a driver still ensure while following the cooling procedure?

    Correct answer: The vehicle is securely prevented from rolling, including suitable chocks.

    The hot-brake caution is not permission to leave a vehicle unsecured. Use a level location, appropriate chocks and the vehicle’s safe parking procedure while the brakes cool.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017): Hot-brake parking exception; physical PDF page 77 (printed 5-9); reviewed September 14, 2026. ↗

  44. Under the cited current FMVSS 121 requirement, ignition is in RUN and service-reservoir pressure is below 60 psi. What must the warning signal do?

    Correct answer: Give a continuous low-air warning.

    S5.1.5 requires a continuous signal other than the gauge below 60 psi with ignition in RUN. It may be visible, or both audible and visible. Applicability depends on the vehicle and the standard in effect when manufactured.

    Source: 49 CFR 571.121, S5.1.5; applicability distinguished by 49 CFR 393.51(c). Official eCFR XML dated September 10, 2026; reviewed September 14, 2026. ↗

  45. For a non-exempt air-braked power unit not subject to FMVSS 121 when manufactured, the governor cuts out at 100 psi. Under 49 CFR 393.51(c)(2), at what pressure and below is continuous warning required?

    Correct answer: 50 psi, the lower of 55 psi and half of cut-out pressure.

    This particular older-vehicle rule uses 55 psi or half the governor cut-out pressure, whichever is less. Half of 100 is 50; do not use this exception as the warning threshold for modern FMVSS 121 vehicles.

    Source: 49 CFR 393.51(c)(2), with paragraph (f) exceptions excluded by the question. Official eCFR XML dated September 10, 2026; reviewed September 14, 2026. ↗

  46. Under the cited FMVSS 121 gauge requirement, what pressure information must be readily visible from the normal driving position?

    Correct answer: The reservoir pressure in each service-brake system.

    S5.1.4 requires a pressure gauge in each service-brake system. The reading is reservoir pressure, and the separate low-air warning is not replaced by the gauge.

    Source: 49 CFR 571.121, S5.1.4; applicability distinguished by 49 CFR 393.51(c). Official eCFR XML dated September 10, 2026; reviewed September 14, 2026. ↗

  47. Under federal commercial-vehicle brake equipment rules, how must corresponding brake chambers on the two ends of an axle compare?

    Correct answer: The service chambers must match in size, and the spring chambers must match in size.

    49 CFR 393.47(b) requires matching service-brake chamber sizes across the axle and matching spring-brake chamber sizes across the axle. It does not say a service chamber and spring chamber must be identical to each other.

    Source: 49 CFR 393.47(b). Official eCFR XML dated September 10, 2026; reviewed September 14, 2026. ↗

  48. Which minimum thickness must commercial-vehicle brake drums and rotors meet under 49 CFR 393.47(g)?

    Correct answer: The limits established by the drum or rotor manufacturer.

    The rule uses the drum or rotor manufacturer’s limits. Do not replace that standard with a guessed universal dimension or a visual impression that the part still looks usable.

    Source: 49 CFR 393.47(g). Official eCFR XML dated September 10, 2026; reviewed September 14, 2026. ↗

  49. What does ABS do when a braked wheel is about to lock?

    Correct answer: It adjusts brake pressure to reduce wheel lockup.

    ABS detects impending lockup and reduces braking pressure as needed. This helps preserve control; it does not replenish the air supply or replace normal brakes.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017), printed 5-4: ABS purpose; physical PDF page 72; reviewed September 14, 2026. ↗

  50. The yellow ABS malfunction lamp stays on after its normal startup check. What should you suspect?

    Correct answer: ABS control may be unavailable at one or more wheels.

    A persistent or newly illuminated ABS fault lamp can indicate lost ABS control. Ordinary braking remains, but the fault needs service; the lamp alone does not identify the failed part.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017), printed 5-4: ABS warning lamp; physical PDF page 72; reviewed September 14, 2026. ↗

  51. Does ABS guarantee a shorter stop in every road condition?

    Correct answer: No; it helps maintain control without guaranteeing a shorter stop.

    ABS primarily helps prevent wheel lockup and retain control. Available traction, speed and other conditions still affect stopping distance.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017), printed 5-4: ABS stopping-distance limits; physical PDF page 72; reviewed September 14, 2026. ↗

  52. A straight truck has working ABS on every axle. In an emergency requiring maximum braking, what does the Ohio manual permit?

    Correct answer: Fully apply the service brakes while maintaining control.

    The handbook explicitly distinguishes working ABS on all axles. Stab braking is not the method for that situation. Keep control and follow the vehicle's instructions.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017), printed 5-8: Braking with full ABS coverage; physical PDF page 76; reviewed September 14, 2026. ↗

  53. On a long downgrade, how should service braking relate to engine braking in the Ohio handbook's method?

    Correct answer: Supplement the engine's braking effect in an appropriate low gear.

    Choose a suitable low gear before descending. The handbook treats service-brake use as a supplement to engine braking, helping prevent overheating.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017), printed 5-9: Engine braking on grades; physical PDF page 77; reviewed September 14, 2026. ↗

  54. In the handbook's downgrade example, your selected safe speed is 40 mph. After applying the brakes for a definite slowdown, at about what speed do you release them?

    Correct answer: 35 mph, about 5 mph below that safe speed.

    The example reduces speed approximately 5 mph below the selected safe speed, then releases the brakes until speed returns to that limit. The example does not establish 40 mph as safe for every grade.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017), printed 5-9: Grade-braking example; physical PDF page 77; reviewed September 14, 2026. ↗

  55. How can repeated heavy service-brake use on a descent reduce braking effectiveness?

    Correct answer: It overheats linings and drums, reducing useful friction and contact.

    Excess heat can change lining friction and expand drums. Continued overuse can cause severe fade or failure, which is why speed, gear and braking technique matter.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017), printed 5-8: Brake fade mechanism; physical PDF page 76; reviewed September 14, 2026. ↗

  56. Several brakes are out of adjustment during a descent. What can happen to the brakes still doing their share?

    Correct answer: They may carry extra workload and overheat.

    When some brakes contribute too little, the others must do more of the work and can fade. Each brake must be in proper condition; one strong brake does not compensate safely for the others.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017), printed 5-8: Uneven brake workload; physical PDF page 76; reviewed September 14, 2026. ↗

  57. In Section 5's stationary released-brake leakage check, a properly secured single vehicle loses 3 psi in one minute. How does that compare with the handbook's criterion?

    Correct answer: It exceeds the less-than-2-psi-per-minute criterion.

    Section 5 distinguishes the released-brake check from the applied check. The released-brake criterion is less than 2 psi per minute for a single vehicle; the applied-test figure must not be substituted.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017), printed 5-6: Released-brake leak check; physical PDF page 74; reviewed September 14, 2026. ↗

  58. Why must you identify which leakage test is being performed before judging the pressure drop?

    Correct answer: Released and fully applied checks use different leakage criteria.

    For the configurations described, Section 5 gives released-test criteria below 2 psi per minute for a single vehicle and below 3 for a combination. The fully applied check allows no more than 3 or 4 respectively after stabilization. Do not mix the setups.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 5 (July 2017), printed 5-6: Released versus applied leakage; physical PDF page 74; reviewed September 14, 2026. ↗

  59. Which sequence matches Ohio's Section 11 air-brake inspection demonstration?

    Correct answer: Gauge/governor cutout, leakage, warning devices, then emergency brakes.

    Section 11 requires these four checks in that order. The complete vehicle-specific setup, rollaway precautions and manufacturer specifications remain necessary.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 11.1.2 (March 2025), printed 11-3: Ohio inspection sequence; physical PDF page 131; reviewed September 14, 2026. ↗

  60. For the air-brake portion of Ohio's vehicle-inspection test, is naming the four checks enough?

    Correct answer: No; the checks must be explained and demonstrated correctly.

    The manual requires both explanation and performance of all four checks in order. Failure to do so results in automatic failure of the vehicle-inspection test; a written quiz does not replace that demonstration.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 11.1.2 (March 2025), printed 11-3: Explaining and demonstrating; physical PDF page 131; reviewed September 14, 2026. ↗

  61. During the emergency-brake check, the vehicle's valves are not designed to pop out. What indication does Ohio's manual tell you to identify?

    Correct answer: The air-discharge sound indicating parking or emergency brake application.

    Ohio describes listening for air discharge on designs whose valves do not pop out. Explain the manufacturer's actual procedure and specifications, not an assumed control movement.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 11.1.2 (March 2025), printed 11-3: Valves without pop-out action; physical PDF page 131; reviewed September 14, 2026. ↗

  62. Under Ohio's Section 11 check for an air-operated trailer, when should its tractor-protection and trailer parking/emergency valves close relative to the power-unit valve?

    Correct answer: At the same time as, or before, the power-unit valve.

    The trailer-related valves should close at the same time or earlier. This is the described inspection relationship; the applicant must also know the equipment's specified activation levels.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 11.1.2 (March 2025), printed 11-3: Trailer emergency-valve timing; physical PDF page 131; reviewed September 14, 2026. ↗

  63. What must you explain about valve pop-out in the primary/secondary air system described by Ohio's Section 11?

    Correct answer: Loss of pressure in only one system does not make the valves pop out.

    The handbook requires explaining the backup and why loss in only one system does not cause pop-out. A backup is not permission to continue with a failed circuit: stop safely and correct the fault.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 11.1.2 (March 2025), printed 11-3: Dual-system backup explanation; physical PDF page 131; reviewed September 14, 2026. ↗

  64. After switching off the engine for Ohio's Section 11 applied-leakage check, which key position is specified?

    Correct answer: Return the key to ON or the battery-charge position.

    The procedure keeps electrical power available with the engine off. Secure the vehicle, release the specified controls, apply the foot brake fully, and time leakage only after the initial gauge drop stabilizes.

    Source: Ohio CDL Driver Manual, HSY 7605 7/26, Section 11.1.2 (March 2025), printed 11-3: Electrical power during leakage demonstration; physical PDF page 131; reviewed September 14, 2026. ↗

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Ohio air brakes practice

64 practice questions on air supply, controls, leak checks, ABS and the Ohio inspection procedure. Start the full question set or choose a 16-question set.

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Study notes and Ohio requirements

Ohio's air-brake knowledge test has 25 questions and requires 20 correct. Our random practice uses those totals, but its questions, four-choice format, immediate explanations and lack of a timer are independent learning features. Air brakes are a licensing restriction issue, not a separate endorsement. Read the examination rule.

Read Ohio's air-brake chapter and the vehicle-specific inspection procedure. The manual is HSY 7605 7/26; its air-brake chapter retains a July 2017 revision and the inspection chapter is revised March 2025. These quizzes are knowledge preparation, not a hands-on demonstration or required training.

Keep warning thresholds separate: Ohio's manual says the warning should activate before pressure drops below 55 psi. The federal questions distinguish the continuous below-60-psi warning for applicable FMVSS 121 equipment with ignition in RUN from the older-vehicle rule in 49 CFR 393.51. That older rule uses 55 psi or half governor cut-out pressure, whichever is less, with its stated exceptions. Do not treat the older threshold as permission to ignore a modern warning. Know the manufacturer's specifications and the examiner's required procedure.

Four checks, in the required order

  1. Gauges and governor cutout: establish rollaway protection, inspect the gauges and identify the manufacturer's cutout level.
  2. Applied leakage: engine off, electrical power on, specified parking/trailer controls released, full foot-brake application. Start the one-minute measurement after the initial drop stabilizes. The described single-vehicle limit is 3 psi; the truck-and-one-air-braked-trailer limit is 4 psi.
  3. Warning devices: with the engine off and power on, reduce pressure as directed and identify when the devices activate.
  4. Emergency brakes: identify the equipment's application level and valve behavior. Some designs do not pop out; explain the specified air-discharge indication and backup system.

You must explain and demonstrate all four correctly. This outline is not the complete safe setup or a substitute for the linked Section 11 instructions. A failed circuit or excessive leak needs correction before driving. The released-brake leakage check in Section 5 has different criteria from the applied check above.

Review L and Z restrictions and other Ohio licensing requirements →