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Vehicle inspection: why, when, and what defects to look for

General Knowledge5 minManual section 2.1.1, 2.1.2, 2.1.3

Inspecting your vehicle is the law, and it protects you and everyone on the road. This lesson covers the kinds of inspection and the defects to look for in tires, wheels, brakes, steering, suspension, exhaust, emergency equipment and cargo.

Why inspect

Safety is the most important reason to inspect — safety for you and for other road users.

Finding a defect early can prevent a breakdown that costs time and money, or worse, a crash caused by that defect.

Federal and state laws require drivers to inspect their vehicles. Federal and state inspectors may also inspect them. If an inspector judges the vehicle unsafe, it is put out of service until it is fixed.

Types of inspection

  • Pre-trip inspection (vehicle inspection) — before driving, to find problems that could cause a crash or breakdown.
  • During a trip — watch gauges for signs of trouble; use your senses (look, listen, smell, feel). When you stop, check the critical items: tires, wheels and rims; brakes; lights and reflectors; brake and electrical connections to the trailer; trailer coupling devices; cargo securement devices.
  • After-trip inspection and report — when you finish a trip, a work day or a tour of duty, on every vehicle you drove. It may include a vehicle condition report listing problems, which helps the motor carrier know when repairs are needed.

Tires

  • Too much or too little air pressure.
  • Bad wear. Front (steering) tires must have at least 4/32 inch of tread depth in each major groove; all other tires need at least 2/32 inch. No fabric (cord) should show through the tread or sidewall.
  • Cuts or other damage; tread separation.
  • Dual tires that touch each other or parts of the vehicle.
  • Mismatched sizes; radial and bias-ply tires used together.
  • Cut or cracked valve stems.
  • Regrooved, recapped or retreaded tires are prohibited on the front wheels of a bus.

Wheels and rims

  • Damaged rims.
  • Rust streaks around wheel nuts can be a sign the nuts have worked loose, so check that they are tight. When a tire has just been changed, stop again soon after and check the nuts once more.
  • Missing clamps, spacers, studs or lugs means danger.
  • Mismatched, bent or cracked lock rings are dangerous.
  • Wheels or rims with welding repairs are not safe.

Brake drums and shoes; steering system

Brakes: drums with cracks; shoes or pads coated with oil, grease or brake fluid; and shoes that are worn too thin, broken or missing.

Steering — look for:

  • missing nuts, bolts, cotter keys or other parts;
  • bent, loose or broken parts such as the steering column, steering gear box or tie rods;
  • with power steering: check hoses, pumps and fluid level, and look for leaks;
  • steering wheel play of more than 10 degrees — about 2 inches of movement at the rim of a 20-inch wheel — makes it hard to steer.

Suspension system

The suspension holds up the vehicle and its load and keeps the axles in place, so broken parts can be extremely dangerous. Look for:

  • spring hangers that let the axle move out of position; cracked or broken spring hangers;
  • missing or broken leaves in any leaf spring — if one-fourth (1/4) or more are missing, the vehicle is put out of service, but any defect can be dangerous;
  • broken leaves in a multi-leaf spring, or leaves that have shifted and might hit a tire or other part;
  • leaking shock absorbers;
  • cracked, damaged or missing torque rod or arm, U-bolts, spring hangers or other axle-positioning parts;
  • damaged and/or leaking air suspension systems;
  • any loose, cracked, broken or missing frame members.

Exhaust system

A broken exhaust can let poison fumes (carbon monoxide) into the cab or sleeper berth. Look for:

  • loose, broken or missing exhaust pipes, mufflers, tailpipes or vertical stacks;
  • loose, broken or missing mounting brackets, clamps, bolts or nuts;
  • exhaust parts rubbing against fuel system parts, tires or other moving parts;
  • exhaust parts that are leaking.

Emergency equipment and cargo

Vehicles must carry emergency equipment:

  • fire extinguisher(s) (properly charged and rated);
  • spare electrical fuses, unless the vehicle has circuit breakers;
  • warning devices for parked vehicles: 3 reflective triangles, or at least 6 fuses, or 3 liquid-burning flares.

Cargo (trucks): before each trip, confirm the truck is not overloaded and that the load is balanced and tied down (secured). If the cargo includes hazardous materials, also check for the proper papers and placards.

References and scope

The topic reference is listed below. Sources support verification; the lesson itself is here. The current content needs technical and language review before public launch.

Manual reference: 2.1.1, 2.1.2, 2.1.3

Official CDL handbook · Utah ↗StatesOur editorial approach

Put it into practice

Educational questions with explanations. The answer review also works without the interactive quiz.

Preparing your questions…

Review questions with answers

  1. The main reason drivers inspect their vehicles is:
    1. To avoid fines
    2. Safety for yourself and other road users
    3. To keep the truck clean
    4. To save fuel
    Show answer
    Safety for yourself and other road users

    Safety is the most important reason to inspect.

  2. If a federal or state inspector judges your vehicle unsafe, they will:
    1. Give you 30 days to fix it
    2. Let you finish the trip first
    3. Only write a warning
    4. Put it out of service until it is fixed
    Show answer
    Put it out of service until it is fixed

    Unsafe vehicles are put "out of service" until repaired.

  3. Which items should you check each time you stop during a trip?
    1. Tires, brakes, lights, trailer connections, coupling and cargo securement
    2. Only the fuel level
    3. Only the radio and air conditioning
    4. Nothing until the end of the day
    Show answer
    Tires, brakes, lights, trailer connections, coupling and cargo securement

    At stops, check tires/wheels/rims, brakes, lights/reflectors, brake and electrical connections, coupling devices and cargo securement.

  4. What is the minimum tread depth for front (steering) tires?
    1. 1/32 inch
    2. 2/32 inch
    3. 4/32 inch
    4. 6/32 inch
    Show answer
    4/32 inch

    Front tires need at least 4/32 inch in every major groove.

  5. What is the minimum tread depth for tires other than the front tires?
    1. 1/32 inch
    2. 2/32 inch
    3. 3/32 inch
    4. 4/32 inch
    Show answer
    2/32 inch

    Other tires need at least 2/32 inch.

  6. Recapped or retreaded tires are prohibited on:
    1. The front wheels of a bus
    2. The rear wheels of a trailer
    3. Any truck
    4. The drive axle of a tractor
    Show answer
    The front wheels of a bus

    Regrooved, recapped or retreaded tires may not be used on a bus's front wheels.

  7. Rust around wheel nuts may mean:
    1. The wheel was just painted
    2. The tire is underinflated
    3. The brakes are overheating
    4. The nuts are loose
    Show answer
    The nuts are loose

    Rust streaks around lug nuts can mean they are loose; check tightness.

  8. After a tire has been changed, you should:
    1. Never touch the nuts again
    2. Stop a short while later and re-check the wheel nuts
    3. Drive at least 500 miles before checking
    4. Add extra air to the new tire only
    Show answer
    Stop a short while later and re-check the wheel nuts

    After a tire change, stop a short while later and re-check nut tightness.

  9. Wheels or rims that have had welding repairs are:
    1. Safe if painted
    2. Required on front axles
    3. Not safe
    4. Safe on trailers only
    Show answer
    Not safe

    Welded wheels or rims are not safe.

  10. Steering wheel play of more than ___ degrees can make it hard to steer.
    1. 10
    2. 5
    3. 20
    4. 30
    Show answer
    10

    More than 10 degrees (about 2 inches at the rim of a 20-inch wheel) is too much play.

  11. On a 20-inch steering wheel, 10 degrees of play is about how much movement at the rim?
    1. Half an inch
    2. 1 inch
    3. 4 inches
    4. 2 inches
    Show answer
    2 inches

    10 degrees is approximately 2 inches at the rim of a 20-inch wheel.

  12. If one-fourth or more of the leaves in a leaf spring are missing, the vehicle:
    1. Can be driven slowly
    2. Will be put out of service
    3. Needs only a warning
    4. Must carry less cargo
    Show answer
    Will be put out of service

    Missing 1/4 or more of the leaves puts the vehicle out of service; any defect can be dangerous.

  13. Why is a broken exhaust system dangerous?
    1. It makes the engine run too cold
    2. It drains the battery
    3. It can let poison fumes into the cab or sleeper berth
    4. It causes the brakes to lock
    Show answer
    It can let poison fumes into the cab or sleeper berth

    A broken exhaust can let poisonous fumes into the cab or sleeper.

  14. Which emergency equipment is required on a CMV?
    1. Fire extinguisher, spare fuses (unless circuit breakers) and warning devices such as 3 reflective triangles
    2. A first-aid kit, flashlight and tow strap
    3. Tire chains and a shovel
    4. A spare tire and a jack
    Show answer
    Fire extinguisher, spare fuses (unless circuit breakers) and warning devices such as 3 reflective triangles

    Required: fire extinguisher(s), spare fuses unless equipped with circuit breakers, and warning devices for parked vehicles.

  15. Instead of 3 reflective triangles, a vehicle may carry:
    1. 2 flashlights
    2. 1 road flare
    3. 4 traffic cones
    4. At least 6 fuses or 3 liquid-burning flares
    Show answer
    At least 6 fuses or 3 liquid-burning flares

    Warning devices: 3 reflective triangles, or at least 6 fuses, or 3 liquid-burning flares.

  16. Which is a tire problem to look for during inspection?
    1. Tires of the same size on the same axle
    2. Radial and bias-ply tires used together
    3. Valve caps in place
    4. Even tread wear
    Show answer
    Radial and bias-ply tires used together

    Mixing radial and bias-ply tires is a defect.

  17. Before each trip, a truck driver must make sure the cargo is:
    1. Covered with a tarp in all cases
    2. Loaded only at the rear
    3. Not overloaded, balanced and secured
    4. Weighed at a public scale
    Show answer
    Not overloaded, balanced and secured

    Before each trip, confirm the truck is not overloaded and the load is balanced and secured; with hazmat, also check papers and placards.

  18. An after-trip inspection should be done:
    1. When a trip, work day or tour of duty ends, on every vehicle you drove
    2. Only once a week
    3. Only if there was a crash
    4. Only by a mechanic
    Show answer
    When a trip, work day or tour of duty ends, on every vehicle you drove

    Do an after-trip inspection at the end of each trip, day or tour of duty on every vehicle you operated.

  19. Which is a steering system defect?
    1. A clean steering wheel
    2. Power steering fluid at the full mark
    3. Tight tie rods
    4. Missing cotter keys or a loose steering gear box
    Show answer
    Missing cotter keys or a loose steering gear box

    Missing nuts, bolts or cotter keys and loose or broken steering parts are defects.

  20. Which brake defect should you look for during an inspection?
    1. Brake drums that feel warm after a drive
    2. Brake hoses with no cracks or wear
    3. Brake shoes or pads with oil, grease or brake fluid on them
    4. Brake shoes with plenty of lining left
    Show answer
    Brake shoes or pads with oil, grease or brake fluid on them

    Look for cracked drums, shoes or pads with oil, grease or brake fluid on them, and shoes worn dangerously thin, missing or broken.

  21. What does the suspension system do?
    1. Holds up the vehicle and its load and keeps the axles in place
    2. Slows the vehicle on downgrades
    3. Keeps the engine cool
    4. Sends power to the drive wheels
    Show answer
    Holds up the vehicle and its load and keeps the axles in place

    The suspension holds up the vehicle and its load and keeps the axles in place, so broken suspension parts can be extremely dangerous.