← CDL Vehicle Inspection - General Knowledge Flashcards

CDL Commercial Drivers License General Knowledge Study Guide

Key concepts, definitions, and exam tips organized by topic.

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CDL Vehicle Inspection – General Knowledge Study Guide


Overview

This study guide covers the essential knowledge required for the CDL Vehicle Inspection section of the General Knowledge exam. It includes pre-trip inspection procedures, federal documentation requirements, en-route and post-trip checks, and critical component standards. Mastering these concepts is essential not only for passing the CDL exam but for maintaining safety on the road.


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Pre-Trip Inspection


Purpose & Frequency

  • • The primary purpose of a pre-trip inspection is to ensure the vehicle is safe to drive before beginning a trip, catching defects that could cause accidents or breakdowns.
  • • A Driver Vehicle Inspection Report (DVIR) must be completed at least once every 24 hours when operating a commercial vehicle.

    • The 7-Step Inspection Method

    The first step is always the approach step:

    1. Step 1 – Approach the Vehicle: Check for visible damage, fluid leaks under the vehicle, and overall condition before entering the cab.

    2. Steps 2–7 cover the engine compartment, in-cab checks, walking around the vehicle, checking lights, and final walk-around.


    > Key Terms:

    > - 7-Step Inspection Method – The standardized sequence for completing a thorough pre-trip inspection

    > - Approach Step – First step; observe vehicle from a distance for damage or leaks


    Engine Compartment Checks

    When inspecting the engine compartment, check the following fluid levels:

  • • Engine oil level
  • • Coolant level
  • • Power steering fluid level

    • Also inspect the alternator belt for:

  • • Cracks or fraying
  • • Excessive looseness (could cause alternator failure and loss of electrical power)

    • > ⚠️ Watch Out For: Students often forget to check power steering fluid — all three fluid levels are required.


    Tire Tread Depth Requirements


    | Tire Location | Minimum Tread Depth |

    |---|---|

    | Front (steering) tires | 4/32 inch |

    | Rear drive tires | 2/32 inch |


    > ⚠️ Watch Out For: Front tires have a stricter standard than rear tires. The exam frequently tests this distinction.


    Steering System

  • • Power steering system with an 18-inch steering wheel: maximum allowable free play is 2 inches.
  • • Excessive free play indicates worn or damaged steering components and is a safety defect.

    • Coupling System (Tractor-Trailers)

  • • Inspect the fifth wheel to confirm it is:

    • - Properly mounted

    - Latched securely around the kingpin

    - Free of missing, bent, or broken parts

  • • Tug Test: Pull forward gently against locked trailer brakes to verify the kingpin is properly secured.

    • > Key Terms:

    > - Fifth Wheel – The coupling device connecting the tractor to the trailer

    > - Kingpin – The pin on the trailer that locks into the fifth wheel

    > - Tug Test – A physical test to confirm the trailer is securely connected


    In-Cab Inspection

  • • The air pressure gauge must read normal operating range — typically 100–125 psi — before the driver begins moving.
  • • Verify all gauges, mirrors, seatbelts, and emergency equipment are in proper condition.

    • Lug Nuts & Wheels

  • • All lug nuts must be present on every wheel — none can be missing or loose.
  • • Missing or loose lug nuts are an automatic out-of-service defect.

    • Windshield & Wipers

    When inspecting the windshield, check for:

  • • Cracks or chips that obstruct the driver's view
  • • Operational windshield wipers
  • • Adequate washer fluid

    • Exhaust System

    Inspect for:

  • • Loose, broken, or missing pipes, mufflers, or mounting brackets
  • • Exhaust leaks near the cab or sleeper berth (carbon monoxide risk)

    • Required Lighting Equipment

    All of the following must be verified as working during the pre-trip inspection:

  • • Headlights
  • • Taillights
  • • Brake lights
  • • Turn signals
  • • Clearance lights
  • • Marker lights
  • • Hazard flashers

    • ---


    Inspection Regulations & Documentation


    Driver Responsibility

  • • The driver is always responsible for inspecting the vehicle and ensuring it is safe before and during operation — not the carrier, mechanic, or dispatcher.

    • Handling the Previous DVIR

    Before starting a trip, the driver must:

    1. Review the previous driver's DVIR

    2. Sign it to confirm that either:

    - Reported defects were repaired, or

    - No repairs were needed

    - The vehicle is confirmed safe to operate


    > ⚠️ Watch Out For: You must sign the previous DVIR even if you didn't drive the vehicle — reviewing and signing is your responsibility.


    DVIR Retention

  • • Motor carriers must retain completed DVIRs for at least 3 months.

    • Required Information on a DVIR

    Every DVIR must include:

  • • Date and time
  • • Location
  • • Vehicle identification (unit number, license plate)
  • • Odometer reading
  • • Condition of specified parts
  • • Driver's signature
  • • Any defects noted

    • When a DVIR is NOT Required

    A DVIR is not required when:

  • • The driver operates the same vehicle for the entire day, and
  • • No defects were found during that operating period

    • > ⚠️ Watch Out For: Both conditions must be true. If a defect is found, a DVIR is always required regardless of circumstances.


    Defects & Out-of-Service Standards

  • • Any defect that could affect safe operation must be noted on the DVIR.
  • • If a defect could affect safe operation, it must be repaired before driving.

    • ---


    En-Route & Post-Trip Inspection


    En-Route Inspection Checkpoints

    During en-route stops, drivers should check:

  • • Tires – heat buildup, proper inflation, damage
  • • Cargo securement – straps, chains, tarps
  • • Lights – brake lights, turn signals
  • • Brakes – performance and heat
  • • Coupling devices – fifth wheel, safety chains

    • Tire Checks on the Road

  • • First check: After the first 25 miles of a trip
  • • Subsequent checks: At each stop thereafter
  • • Look for: heat buildup, inflation issues, and physical damage

    • Overheating Tire Protocol

  • • If a tire is extremely hot to the touch, do NOT continue driving.
  • • Allow the tire to cool completely before proceeding.
  • • Investigate the cause of overheating.
  • • White smoke from a tire = immediate stop required; indicates possible dragging brake, bearing failure, or critically low inflation.

    • > ⚠️ Watch Out For: White smoke is a critical emergency sign — the exam may test whether you know to stop immediately vs. continuing to the next stop.


    Post-Trip Inspection

  • • Purpose: To identify defects that developed during the trip so they can be reported and repaired before the vehicle's next use.
  • • Post-trip findings must be documented on a DVIR.

    • ---


    Critical Vehicle Components


    Brake System


    #### Brake Fade

  • • Brake fade = loss of braking power due to overheated brakes
  • • Typically caused by prolonged or excessive brake use going downhill
  • • Prevention: Use engine braking and proper downhill gear selection

    • #### Brake Lining Thickness


    | Axle Type | Minimum Lining Thickness |

    |---|---|

    | Non-steering axles | 1/4 inch |


  • • Less than 1/4 inch on a non-steering axle requires immediate replacement.

    • #### Spring Brake Test

    To verify spring brakes are working:

    1. Turn engine off

    2. Fan the brakes (repeatedly press the brake pedal) to reduce air pressure

    3. Spring brakes should automatically engage when pressure drops to 20–45 psi


    > Key Terms:

    > - Brake Fade – Overheating-caused loss of braking power

    > - Spring Brakes – Emergency/parking brakes that engage automatically when air pressure is lost

    > - Fanning the Brakes – Rapidly pressing the brake pedal to reduce air pressure for testing


    Suspension System

  • • A broken or missing leaf spring, or one that has shifted out of place, is an out-of-service defect.
  • • Out-of-service defects mean the vehicle cannot be driven until repaired.

    • > ⚠️ Watch Out For: Not all spring damage is equal on the road, but any broken, missing, or shifted leaf spring is an automatic out-of-service condition on the exam.


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    Key Terms Master List


    | Term | Definition |

    |---|---|

    | DVIR | Driver Vehicle Inspection Report — required documentation of vehicle condition |

    | Pre-Trip Inspection | Safety check performed before beginning any trip |

    | Out-of-Service Defect | A defect serious enough to prohibit operating the vehicle |

    | Fifth Wheel | Coupling device on the tractor that connects to the trailer |

    | Kingpin | Trailer pin that locks into the fifth wheel |

    | Tug Test | Test to verify trailer/tractor connection is secure |

    | Brake Fade | Loss of braking effectiveness due to overheating |

    | Spring Brakes | Automatic emergency brakes activated by low air pressure |

    | Tread Depth | Measurement of remaining rubber on a tire |

    | Free Play | Slack in the steering wheel before wheels begin to turn |

    | Air Pressure | Compressed air that powers the braking system (100–125 psi normal) |


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    Watch Out For — Common Exam Pitfalls


  • • ⚠️ Front vs. rear tire tread: Front = 4/32", Rear = 2/32". Don't mix these up.
  • • ⚠️ Who is responsible? Always the driver — not the company or mechanic.
  • • ⚠️ DVIR retention = 3 months, not 6 months or 1 year.
  • • ⚠️ Spring brakes engage when air pressure drops to 20–45 psi — know this range.
  • • ⚠️ White smoke from a tire = stop immediately — never continue driving.
  • • ⚠️ Tug test confirms kingpin connection — this is different from a brake test.
  • • ⚠️ All lug nuts must be present — even one missing is a defect.
  • • ⚠️ DVIR not required only when same vehicle + no defects found — both conditions required.
  • • ⚠️ First en-route tire check is at 25 miles, not 50 or 100.
  • • ⚠️ Exhaust leaks near the cab are dangerous due to carbon monoxide poisoning risk.

    • ---


    Quick Review Checklist


    Before your exam, confirm you can answer each of the following:


  • • [ ] State the primary purpose of a pre-trip inspection
  • • [ ] Identify the first step in the 7-step inspection method
  • • [ ] Recall the three fluid levels checked in the engine compartment
  • • [ ] State tread depth requirements for front tires (4/32") and rear tires (2/32")
  • • [ ] Explain what the tug test is and what it verifies
  • • [ ] Describe how to test spring brakes (fan brakes to 20–45 psi)
  • • [ ] State the minimum brake lining thickness for non-steering axles (1/4 inch)
  • • [ ] Explain what brake fade is and its cause
  • • [ ] Know that DVIRs must be retained for 3 months
  • • [ ] Know all required information on a DVIR
  • • [ ] Identify when a DVIR is not required
  • • [ ] Know that white smoke from a tire = immediate stop
  • • [ ] Confirm that first en-route tire check is at 25 miles
  • • [ ] State normal air pressure range before driving (100–125 psi)
  • • [ ] Know that a broken leaf spring is an out-of-service defect
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