General Knowledge test

CDL Vehicle Inspection Questions

Vehicle inspection is the one topic that shows up twice in the CDL process. It is examined on the General Knowledge written test, and then you have to perform a pre-trip inspection out loud in front of an examiner during the skills test. Most of the written questions are less about naming parts and more about knowing what you are looking for and what makes a defect serious enough to keep the truck off the road.

What the test asks about vehicle inspection

Federal rules require a driver to inspect the vehicle before driving and to file a written report at the end of the day when defects are found. That is why examiners lean on this topic: an inspection question is really a question about whether you would notice a cracked leaf spring, an audible air leak, or a loose lug nut before you got moving. Drivers who treat the inspection as a memorized script tend to pass the written test and then struggle on the skills test, because the examiner asks why, not just what.

Where drivers lose marks

  • Learning the inspection as a list of part names instead of a repeatable route around the vehicle, which falls apart the moment the examiner starts asking questions out of order.
  • Not knowing which defects put a vehicle out of service. Cracked or missing parts on the steering and braking systems, bald or badly cut tires, and leaking fluid lines are not cosmetic issues.
  • Forgetting the in-cab portion. Gauges, the parking brake check, mirrors, horn, wipers, and emergency equipment all appear on the written test.
  • Skipping the post-trip inspection and the driver vehicle inspection report, which the test does ask about.

How to study itWork through the questions below, then walk an actual truck if you can get access to one. Say each step out loud in the same order every time. The written questions get much easier once the route is muscle memory rather than a list.

50 Vehicle Inspection practice questions with answers

Every question below is followed by the correct answer and an explanation of why it is right. Read through them, then take the timed General Knowledge test to see how you do without the answers in front of you.

1. What is the proper 'safe start' procedure when preparing to start a manual transmission commercial vehicle?

  • A. Put the vehicle in a high gear and turn the key.
  • B. Depress the clutch completely, put the gearshift in neutral, and then start the engine. (correct answer)
  • C. Start the engine without touching the pedals to save wear on the clutch.
  • D. Hold the brake, put it in first gear, and start the engine.

Why: A safe start requires fully depressing the clutch pedal, ensuring the transmission is in neutral, and then turning the key. This prevents the vehicle from lurching forward upon starting.

2. When inspecting the drive shaft, what should you specifically check?

  • A. That the shaft is perfectly straight and the U-joints are secure and free of foreign objects. (correct answer)
  • B. That the shaft is heavily coated in thick grease.
  • C. That there is at least 2 inches of horizontal play in the shaft.
  • D. That the U-joints have safety wire wrapped around them.

Why: The drive shaft should not be bent or cracked. The universal joints (U-joints) should appear secure, intact, properly lubricated, and free of any debris like wire or twine wrapped around them.

3. What should you check regarding the retro-reflective tape (conspicuity tape) on your vehicle?

  • A. That it covers the entire surface area of the trailer.
  • B. That it is clean, securely affixed, and placed correctly along the sides and rear. (correct answer)
  • C. That it is purely white in color.
  • D. That it only reflects light from high-beam headlights.

Why: Retro-reflective tape must be clean, not peeling, and clearly visible. It is required along the sides and rear of commercial trailers to enhance visibility at night.

4. Which of the following items are considered mandatory emergency equipment that must be carried on all commercial motor vehicles?

  • A. A first aid kit, a high-visibility vest, and a flashlight.
  • B. Fire extinguisher, spare electrical fuses, and warning devices for parked vehicles. (correct answer)
  • C. A GPS navigation system, spare tire, and basic tool kit.
  • D. Jumper cables, tire chains, and a reflective safety jacket.

Why: Federal regulations mandate that commercial vehicles carry a properly rated fire extinguisher, spare electrical fuses (unless equipped with circuit breakers), and warning devices such as three reflective triangles.

5. According to the seven-step pre-trip inspection method, what is the very first step?

  • A. Check the engine compartment.
  • B. Start the engine and inspect inside the cab.
  • C. Review the last vehicle inspection report. (correct answer)
  • D. Perform a walk-around inspection.

Why: Step 1 of the recommended seven-step inspection method is to review the last Driver Vehicle Inspection Report (DVIR) to ensure any defects noted previously have been repaired.

6. What is the standard rule regarding welding repairs on commercial vehicle wheel rims?

  • A. Welding is permitted if done by a certified mechanic.
  • B. Welding is strictly prohibited; damaged rims must be replaced. (correct answer)
  • C. Welding is allowed only on steel rims, not aluminum.
  • D. Welding is allowed if the crack is less than 2 inches long.

Why: Welding repairs on wheel rims are completely prohibited. A cracked or damaged rim must be replaced, as welding compromises the structural integrity.

7. What must you check when inspecting the driver's seatbelt?

  • A. That it matches the color of the interior.
  • B. That it has an automatic retractor mechanism.
  • C. That it is securely mounted, latches properly, and the webbing is not frayed or ripped. (correct answer)
  • D. That it stretches at least 5 inches when pulled.

Why: The safety belt must be securely mounted to the seat/cab, latch and unlatch properly, and the webbing material must not be cut, frayed, or structurally degraded.

8. During the pre-trip inspection, what is the main requirement regarding the mirrors?

  • A. They must have convex additions.
  • B. They must be heated mirrors.
  • C. They must be clean, not cracked, firmly mounted, and adjusted properly from the driver's seat. (correct answer)
  • D. They must be folded inward before starting the trip.

Why: All required mirrors must be securely mounted, clean, free of cracks that obstruct vision, and properly adjusted to give the driver a clear view of the blind spots.

9. At the end of a driving day, federal regulations require drivers of commercial vehicles to do what?

  • A. Wash the vehicle completely.
  • B. Complete a written Driver Vehicle Inspection Report (DVIR) for each vehicle operated. (correct answer)
  • C. Drain the fuel tanks to prevent theft.
  • D. Leave the vehicle running for 10 minutes to cool down.

Why: Drivers must prepare a written or electronic Driver Vehicle Inspection Report (DVIR) at the end of each workday for every vehicle they operated, noting any defects that could affect safety.

10. During your pre-trip inspection, how many horns must be working on a commercial motor vehicle if it is equipped with both a city and an air horn?

  • A. Only the air horn.
  • B. Only the city horn.
  • C. Any horn as long as one works.
  • D. Both the city horn and the air horn must be fully operational. (correct answer)

Why: If a vehicle is equipped with both a standard city horn and a pneumatic air horn, both must be tested during the pre-trip inspection and both must operate properly.

11. After starting a trip, within how many miles must a driver stop to inspect the cargo and its securement devices?

  • A. 25 miles
  • B. 50 miles (correct answer)
  • C. 100 miles
  • D. 150 miles

Why: Federal regulations require drivers to perform an initial en-route inspection of their cargo and securement devices within the first 50 miles of beginning a trip.

12. How do you test the turn signals during a pre-trip walk-around inspection?

  • A. Honk the horn and observe if the lights flash.
  • B. Turn on the four-way flashers to check all signal lights at once, then verify left and right signals individually in the cab. (correct answer)
  • C. Turn the steering wheel all the way left, then right.
  • D. Ask a mechanic to hook up a diagnostic tool.

Why: Drivers commonly use the four-way hazard flashers to visually inspect all external turn signal bulbs simultaneously during the walk-around, and later check the individual left and right dash indicators from the cab.

13. During your walk-around inspection, you see rust trails emanating from the lug nuts on a wheel. What does this usually indicate?

  • A. The wheel was recently washed with nuclear chemicals.
  • B. The lug nuts are overtightened and stripping the threads.
  • C. The lug nuts are loose. (correct answer)
  • D. The brake drum is overheating.

Why: Rust trails around lug nuts are a primary visual indicator that the lug nuts are loose and backing off the studs. They should be tightened to the manufacturer's specifications.

14. When looking at the shock absorbers during a suspension inspection, what is a primary sign that they need replacing?

  • A. They are cold to the touch after driving.
  • B. They have fluid leaking down the outside of the shock casing. (correct answer)
  • C. They are mounted vertically instead of diagonally.
  • D. They compress when the vehicle goes over a bump.

Why: A wet or oily casing on a shock absorber indicates that the internal hydraulic fluid is leaking out. A leaking shock is defective and needs to be replaced.

15. During your in-cab inspection, why is it necessary to check the heater and defroster?

  • A. To ensure driver comfort during long hauls.
  • B. To keep the engine coolant circulating properly.
  • C. To ensure you can keep the windshield clear of frost, ice, and fog. (correct answer)
  • D. It is not a mandatory part of the CDL inspection.

Why: Checking the heater and defroster is a critical safety item. A working defroster is required to clear the windshield of ice, frost, and condensation for safe visibility.

16. When you start the engine, how long should it take for the oil pressure gauge to come up to normal?

  • A. Immediately.
  • B. Within seconds. (correct answer)
  • C. About 1 to 2 minutes.
  • D. It may not rise until the engine is fully warmed up.

Why: The oil pressure gauge must come up to normal within seconds after the engine starts. If it does not, the engine should be shut down immediately to prevent severe damage.

17. Which of the following statements about tire sizes on a commercial vehicle is true?

  • A. Mismatched sizes are acceptable as long as they are on the same side of the vehicle.
  • B. You cannot mix tire sizes on the same axle. (correct answer)
  • C. Front tires must always be larger than rear tires.
  • D. Radial and bias-ply tires can be mixed freely on duals.

Why: Tires on the same axle must be of the same size and type. Mixing tire sizes on the same axle or mixing radial and bias-ply tires on a dual assembly causes severe handling and structural issues.

18. During your in-cab inspection, the air pressure should build from 85 psi to 100 psi within approximately how many seconds (at operating RPM)?

  • A. 15 seconds
  • B. 45 seconds (correct answer)
  • C. 60 seconds
  • D. 120 seconds

Why: For most standard air brake systems at operating RPM, pressure should build from 85 to 100 psi within 45 seconds. If it takes longer, the compressor may be failing or there is an air leak.

19. How much steering wheel free play is considered unacceptable and a potential safety defect on a vehicle equipped with a 20-inch power steering wheel?

  • A. More than 5 degrees (1 inch)
  • B. More than 10 degrees (2 inches) (correct answer)
  • C. More than 15 degrees (3 inches)
  • D. More than 20 degrees (4 inches)

Why: According to the CDL manual, steering wheel free play of more than 10 degrees (which is approximately 2 inches of movement at the rim of a 20-inch steering wheel) can make it difficult to steer and is considered an out-of-service defect.

20. What is the minimum tread depth required for all tires on a commercial vehicle other than the front tires?

  • A. 2/32 of an inch (correct answer)
  • B. 4/32 of an inch
  • C. 1/32 of an inch
  • D. 3/32 of an inch

Why: For all tires except the front tires (such as drive and trailer tires), the minimum required tread depth is 2/32 of an inch in every major groove.

21. What are the requirements for the windshield wipers during a pre-trip inspection?

  • A. They must have winter blades installed year-round.
  • B. They must operate smoothly, arms must be secure, and rubber blades must be pliable and not torn. (correct answer)
  • C. They must have built-in washer fluid sprayers.
  • D. Only the driver side wiper is required by law to work.

Why: Both windshield wipers must operate properly. The arms must be secure, and the rubber blades must not be stiff, cracked, or torn, ensuring they make good contact with the windshield.

22. If you observe black carbon soot on the outside of your exhaust system components, what is this a sign of?

  • A. The engine is burning too much oil.
  • B. The diesel exhaust fluid (DEF) tank is empty.
  • C. There is a leak in the exhaust system. (correct answer)
  • D. The vehicle is operating at peak efficiency.

Why: Black carbon soot visible on exhaust piping, clamps, or mufflers is a clear visual indicator of an exhaust leak, which can allow dangerous carbon monoxide into the cab.

23. When inspecting dual tires, what is a crucial element to look for between the wheels?

  • A. That the mud flap is touching both tires.
  • B. That the inner rims are welded together.
  • C. That there is proper spacing, the tires are not touching, and there is no debris lodged between them. (correct answer)
  • D. That there is a cross-tread pattern connecting them.

Why: When inspecting dual tires, you must verify they are evenly spaced, not touching each other, and that no rocks or debris are wedged between them.

24. What is the safest way to check the coolant level on a hot engine?

  • A. Slowly loosen the radiator cap with bare hands.
  • B. Check the transparent coolant recovery tank or sight glass. (correct answer)
  • C. Pour cold water over the radiator before opening the cap.
  • D. Wait 5 minutes, then quickly remove the cap.

Why: Never open a radiator cap on a hot engine. The safest way is to visually inspect the transparent coolant reservoir tank. If you must open the cap, you must wait until the engine has completely cooled.

25. When inspecting an air ride suspension system, what indicates a critical defect?

  • A. Airbags that are slightly dusty.
  • B. Airbags that are deflated, cut, or leaking air. (correct answer)
  • C. Hearing the leveling valve exhaust air momentarily.
  • D. Rubber mounts that are black in color.

Why: Air suspension systems rely on intact airbags. Any cuts, bulges, deflation, or audible air leaks in the airbags or lines are critical defects that require immediate repair.

26. When inspecting mud flaps (splash guards) what criteria must they meet?

  • A. They must drag on the ground at all times.
  • B. They must be securely mounted and not be missing, torn, or hanging too high off the ground. (correct answer)
  • C. They must be customized with the company logo.
  • D. They are only required on the front wheels.

Why: Mud flaps must be securely attached, undamaged (not excessively torn), and hang at the proper height to prevent road debris from being thrown into following traffic.

27. What is the minimum allowable tread depth for front tires on a commercial vehicle?

  • A. 2/32 of an inch
  • B. 4/32 of an inch (correct answer)
  • C. 6/32 of an inch
  • D. 1/8 of an inch

Why: Federal regulations require a minimum of 4/32 of an inch of tread depth in every major groove on front tires. Driving with less is a severe safety hazard and illegal.

28. When inspecting brake drums, a crack is considered critical and puts the vehicle out of service if it exceeds what length?

  • A. One-fourth the width of the friction area.
  • B. One-half the width of the friction area. (correct answer)
  • C. Three-fourths the width of the friction area.
  • D. Any crack visible to the naked eye puts it out of service.

Why: Brake drums (or rotors) must not have cracks longer than one-half the width of the friction area. If they do, they are structurally compromised.

29. How do you properly test the service brakes on your vehicle?

  • A. Drive at 20 mph and perform an emergency stop to see if the wheels lock up.
  • B. Pump the brake pedal three times while parked and hold for 5 seconds.
  • C. Pull forward at 5 mph, apply the service brake firmly, and check to see if the vehicle pulls to either side. (correct answer)
  • D. Rev the engine in neutral and press the brake to check the air pressure drop.

Why: To test the service brakes, you should release the parking brake, move forward at about 5 mph, and apply the service brake firmly. Note any delayed stopping action, unusual feel, or pulling to one side.

30. When turning on the ignition of a vehicle equipped with an Anti-lock Braking System (ABS), what should the yellow ABS indicator light on the dashboard do?

  • A. Stay on continuously while the engine is running.
  • B. Turn on momentarily and then go out. (correct answer)
  • C. Flash rapidly until the vehicle reaches 5 mph.
  • D. Remain off completely unless there is a fault.

Why: The yellow ABS malfunction lamp should illuminate momentarily when the vehicle is first turned on as a bulb check, and then go out, indicating the system is functioning normally.

31. How should you check the hub oil level on a wheel equipped with a sight glass?

  • A. Remove the hub cap and insert a dipstick.
  • B. Look through the sight glass to ensure the oil is above the minimum line. (correct answer)
  • C. Tap the hub with a mallet to listen for a hollow sound.
  • D. Hub oil never needs to be checked if there are no visible leaks.

Why: If the wheel hub has a sight glass, you can visually check that the oil level is adequate (above the minimum fill line). If it doesn't have a sight glass, you must remove the rubber plug to check.

32. If your vehicle is not transporting hazardous materials, what is the minimum required rating for the fire extinguisher?

  • A. 5 B:C (correct answer)
  • B. 10 B:C
  • C. 15 B:C
  • D. 20 A:B:C

Why: A commercial motor vehicle not transporting hazardous materials requires a fire extinguisher with a minimum rating of 5 B:C. Vehicles with hazardous materials require a 10 B:C or higher.

33. When checking the belts in the engine compartment, what is the maximum allowable deflection (play) when you press on the center of the belt?

  • A. Up to 1/4 inch
  • B. Up to 3/4 inch (correct answer)
  • C. Up to 1 and 1/2 inches
  • D. Up to 2 inches

Why: Engine belts (alternator, water pump, air compressor) should be tight. When pressing on the middle of the belt, it should deflect no more than 1/2 to 3/4 of an inch.

34. What color must the clearance lights, identification lights, and reflectors be on the rear of a commercial vehicle?

  • A. Amber
  • B. Red (correct answer)
  • C. White
  • D. Yellow

Why: All lights and reflectors facing the rear of a commercial motor vehicle (except backup lights and license plate lights) must be red.

35. If you check the battery box and notice that the cell caps are missing, what should you do?

  • A. Add distilled water and leave them open.
  • B. Cover the holes with duct tape.
  • C. Consider it a defect; battery caps must be present and secure. (correct answer)
  • D. Nothing, modern batteries are designed to vent freely.

Why: Battery cell caps must be securely in place. Missing caps allow dangerous battery acid to spill out, which is a significant safety defect.

36. When inspecting the fuel tank, what specific elements must you verify?

  • A. That the tank is full to the brim.
  • B. That the tank is painted red to indicate fuel.
  • C. That the tank is securely mounted, there are no leaks from the tank or lines, and the fuel cap is tight. (correct answer)
  • D. That the fuel lines are made of copper.

Why: A proper fuel tank inspection ensures the mounting brackets/straps are tight, there are no visible fuel leaks, and the fuel cap is securely fastened to prevent spillage.

37. For a standard commercial vehicle with air drum brakes, brake linings must NOT be thinner than what measurement?

  • A. 1/16 of an inch
  • B. 1/8 of an inch
  • C. 1/4 of an inch (correct answer)
  • D. 1/2 of an inch

Why: Standard commercial drum brake linings must not be thinner than 1/4 of an inch. If they are worn below this limit, the vehicle is unsafe and typically placed out of service.

38. What does a functional voltmeter or ammeter verify during your in-cab inspection?

  • A. The air pressure is at a safe level.
  • B. The alternator is charging the battery and the electrical system is operating normally. (correct answer)
  • C. The headlights are turned on.
  • D. The engine oil is at the proper temperature.

Why: The voltmeter or ammeter gauge shows whether the alternator is actively generating electricity and charging the batteries while the engine is running.

39. During a brake inspection, which type of contamination on the brake linings puts the vehicle out of service?

  • A. Light road dust.
  • B. Water from driving in the rain.
  • C. Grease, oil, or brake fluid saturating the friction material. (correct answer)
  • D. Surface rust on the outer edges.

Why: Brake linings that are soaked in grease, oil, or brake fluid cannot provide the necessary friction to stop the vehicle and are considered a dangerous, out-of-service defect.

40. Which of the following are components of the steering linkage that must be inspected for wear and security?

  • A. The U-bolts and spring hangers.
  • B. The pitman arm, drag link, and tie rod. (correct answer)
  • C. The slack adjuster and S-cam.
  • D. The universal joints and carrier bearing.

Why: The steering linkage consists of parts that connect the steering box to the wheels, specifically the pitman arm, drag link, steering knuckle, and tie rod. These must not be loose or missing any cotter pins.

41. While inspecting the frame of the vehicle, which of the following is considered an out-of-service defect?

  • A. Factory-drilled holes in the frame rail.
  • B. Light surface rust on the cross members.
  • C. Cracks, unauthorized welds, or broken cross members. (correct answer)
  • D. A frame that is painted a different color than the cab.

Why: Any longitudinal frame member that is cracked, bent, or has unauthorized welds is a critical structural failure and places the vehicle out of service.

42. How often must you stop to inspect your vehicle and cargo while in transit?

  • A. Every 100 miles or 2 hours, whichever comes first.
  • B. Every 150 miles or 3 hours, whichever comes first. (correct answer)
  • C. Every 200 miles or 4 hours, whichever comes first.
  • D. Only when you stop for fuel or meals.

Why: After the initial 50-mile check, cargo and securement must be inspected every 150 miles or every 3 hours of driving, whichever comes first.

43. When checking a manual slack adjuster on an S-cam brake system, how far should the pushrod move when pulled hard by hand with the brakes released?

  • A. Not more than 1 inch. (correct answer)
  • B. Not more than 2 inches.
  • C. Between 1.5 and 2.5 inches.
  • D. It should not move at all.

Why: With the vehicle safely chocked and parking brakes released, pulling hard on the manual slack adjuster should result in no more than 1 inch of pushrod travel. More than 1 inch indicates the brakes need adjustment.

44. Which of the following conditions regarding the vehicle's windshield is a safety defect?

  • A. Small chips outside the driver's normal line of sight.
  • B. Cracks that obscure the driver's forward vision. (correct answer)
  • C. An inspection sticker placed in the lower corner of the passenger side.
  • D. A light layer of road dust that can be cleared by wipers.

Why: Any cracks, pitting, or damage that obscures the driver's vision through the windshield is a critical safety defect and must be repaired.

45. During your pre-trip inspection, what should you verify regarding the cargo securement?

  • A. That all tie-downs are loosely fastened to allow for load shifting.
  • B. That the cargo is pushed entirely against the right side of the trailer.
  • C. That the cargo is properly blocked, braced, tied down, and that there are an adequate number of securement devices. (correct answer)
  • D. Cargo securement is only the responsibility of the warehouse staff, not the driver.

Why: The driver is ultimately responsible for ensuring the load is adequately secured, blocked, and braced using a sufficient number of undamaged tie-downs before driving.

46. When inspecting your emergency warning triangles, what condition should they be in?

  • A. They must be painted bright yellow.
  • B. They must be unbroken, stable, and have clean reflective surfaces. (correct answer)
  • C. They must have functional battery-powered flashing lights attached.
  • D. They can be broken as long as all three are present.

Why: Warning triangles must be in good working condition. They must stand up securely without falling over, not be broken, and have highly reflective surfaces to warn oncoming traffic.

47. What color must the clearance lights and reflectors on the front of a commercial vehicle be?

  • A. Red
  • B. White
  • C. Amber (correct answer)
  • D. Blue

Why: Federal motor vehicle safety standards mandate that clearance lights, identification lights, and reflectors on the front of the vehicle must be amber.

48. How should you correctly test the parking brake on your vehicle?

  • A. Drive at 10 mph and pull the parking brake valve.
  • B. Apply the parking brake, put the vehicle in a low gear, and gently pull against it. (correct answer)
  • C. Release the parking brake and check if the vehicle rolls on a flat surface.
  • D. Pump the brake pedal until the parking brake pops out.

Why: To test the parking brake, apply it, place the vehicle in a low gear, and gently pull against the brake. The vehicle should not move, indicating the brake holds the vehicle.

49. During your pre-trip inspection, you notice a missing leaf in a leaf spring. At what point does this place the vehicle out of service?

  • A. If one-fourth (1/4) or more of the leaves in any spring assembly are missing. (correct answer)
  • B. If one-half (1/2) or more of the leaves in any spring assembly are missing.
  • C. Only if the main load-bearing leaf is missing.
  • D. If any single leaf is missing, regardless of the total number.

Why: A vehicle is placed out of service if one-fourth (1/4) or more of the leaves in any leaf spring assembly are broken or missing, though even one missing leaf is a dangerous defect that should be fixed.

50. Which of the following statements regarding regrooved, retreaded, or recapped tires is true?

  • A. They are allowed on all axles if properly inflated.
  • B. They are strictly prohibited on the front steering axle of a bus, but allowed on trucks.
  • C. They are prohibited on the front steering axle of any commercial motor vehicle. (correct answer)
  • D. They can only be used during winter months for better traction.

Why: The CDL manual strictly prohibits the use of regrooved, recapped, or retreaded tires on the front steering wheels of any commercial bus or truck.

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