Fleet Maintenance Glossary: Terms Defined

49 CFR: Title 49 of the US Code of Federal Regulations, which holds federal transportation rules. The Federal Motor Carrier Safety Regulations sit in its parts 390 to 399. The official text is on the eCFR.
Annual inspection (periodic inspection): The inspection every commercial motor vehicle must pass at least once in the preceding 12 months, covering at least the components in Appendix A to Part 396, with documentation carried on the vehicle (49 CFR 396.17). The inspection report is kept for 14 months (49 CFR 396.21). See the annual DOT inspection.
Appendix A to Part 396 (formerly Appendix G): The minimum periodic inspection standards: the list of components and the conditions under which a vehicle does not pass its annual inspection. It was published as Appendix G until FMCSA renamed it Appendix A in 2021, and older forms and guides still use the old name.
Base jurisdiction: Under IFTA, the member state or province where a carrier's qualified vehicles are registered, where its operational records are kept or available, and where the fleet travels some of its miles. The carrier licenses and files there.
BASIC: Behavior Analysis and Safety Improvement Category: one of the categories into which FMCSA's Safety Measurement System groups a carrier's inspection and crash data. Vehicle defects found at roadside fall in the Vehicle Maintenance BASIC.
CMV (commercial motor vehicle): Under 49 CFR 390.5, a vehicle used on a highway in interstate commerce to carry passengers or property that has a GVWR, GCWR, gross vehicle weight or gross combination weight of 10,001 pounds or more (whichever is greater); is designed or used to carry more than 8 passengers including the driver for compensation, or more than 15 not for compensation; or carries hazardous materials in a quantity that requires placards.
Combination vehicle: A power unit and the trailer or trailers it tows. For the annual inspection each unit in the combination counts as a vehicle and is inspected on its own.
Component warranty: A warranty on a part fitted to a vehicle, such as an engine, transmission, battery or tire, separate from the vehicle's own warranty and often with its own time or distance limit. See fleet warranty claims.
Cost per mile: Maintenance or running cost divided by miles driven over the same period, used to compare vehicles and to decide when to replace one. Equipment that works standing still is often measured per engine hour instead. See cost per mile.
CSA (Compliance, Safety, Accountability): FMCSA's safety compliance and enforcement program. It uses roadside inspection, crash and investigation data to identify carriers for intervention.
CVSA (Commercial Vehicle Safety Alliance): A nonprofit association of commercial vehicle enforcement officials in North America. It publishes the inspection procedures and out-of-service criteria that roadside inspectors use. See roadside inspections.
Defect (deficiency): A fault in a part or accessory that would affect safe operation or cause a breakdown. A driver must list it on the DVIR, and the carrier must repair it, or certify that repair is unnecessary, before the vehicle runs again (49 CFR 396.11).
Downtime: Time a vehicle cannot work because it is broken down, waiting for parts or out of service. Preventive maintenance trades a little planned downtime for less unplanned downtime.
Driver Vehicle Examination Report: The report FMCSA personnel use to record the results of a roadside vehicle inspection (49 CFR 396.9). Not to be confused with the driver's own DVIR.
Due soon: A service or inspection that is approaching its interval: within a set number of miles, engine hours or days of falling due. The warning window gives time to book the work before the vehicle is overdue.
DVIR (driver vehicle inspection report): The written report a driver prepares at the end of each day's work on each vehicle driven, listing any defect found in the brakes, steering, lights, tires, horn, wipers, mirrors, coupling devices, wheels and rims, and emergency equipment. Under 49 CFR 396.11 a report is required only when a defect is found or reported, must be signed, and is kept for three months. Carriers operating only one commercial motor vehicle are exempt. See DVIR requirements.
ECM (engine control module): The vehicle's engine computer. It records distance, engine hours, fuel used and fault codes, and its odometer reading is accepted for IFTA distance records.
ELD (electronic logging device): A device or technology that automatically records a driver's driving time and supports accurate recording of hours of service, and meets the technical requirements of the rules (49 CFR 395.2).
Engine hours: The running time recorded by the engine's hour meter or ECM. Service intervals for vehicles that idle a lot, and for equipment such as reefers and loaders, are often set in engine hours rather than miles.
Fill-to-fill: Measuring fuel economy between two full fills: miles driven between them divided by the gallons added at the second. Partial fills in between add to the next full fill. See fuel economy and IFTA.
FMCSA (Federal Motor Carrier Safety Administration): The agency of the US Department of Transportation that regulates commercial motor vehicle safety and writes the FMCSRs.
FMCSRs (Federal Motor Carrier Safety Regulations): The federal safety rules for motor carriers, drivers and vehicles, in 49 CFR parts 390 to 399. Part 393 covers parts and accessories, part 395 hours of service and part 396 inspection, repair and maintenance.
GCWR (gross combination weight rating): Under 49 CFR 390.5, the greater of the value the power unit's manufacturer specifies on its certification label, or the sum of the GVWRs or gross weights of the power unit and the units it tows that produces the highest value.
GVWR (gross vehicle weight rating): The maximum loaded weight of a single vehicle, as specified by its manufacturer (49 CFR 390.5). It decides whether a vehicle is a CMV, whatever it actually weighs on the day.
Hubodometer: A distance counter mounted on a wheel hub, common on trailers that have no odometer of their own. Its readings are accepted for IFTA distance records.
Idle time: Time the engine runs while the vehicle is not moving. It burns fuel and adds engine hours without adding miles, so heavy idlers come due for hour-based service sooner.
IFTA (International Fuel Tax Agreement): The agreement among US states and Canadian provinces that lets a carrier license in one base jurisdiction and file one quarterly fuel tax return covering all member jurisdictions. Records are kept for four years. See fuel economy and IFTA.
IFTA decal: The decal issued each year for each qualified vehicle, at least two per vehicle, displayed on the exterior of both sides of the cab. A copy of the IFTA license is carried in the vehicle as well.
Interstate commerce: Transportation between a place in one state and a place outside it, between two places in a state through another state or country, or within a state as part of a movement that starts or ends outside it (49 CFR 390.5). Transportation that is none of these is intrastate commerce, which state rules govern.
Interval: The distance, engine hours or time between two services of the same kind, for example every 25,000 miles, 500 hours or six months. When several limits are set, the service is due at whichever comes first.
Major tread groove: A main groove in a tire's tread pattern, where tread depth is measured. Measurements are not taken on tie bars, humps or fillets (49 CFR 393.75).
Motor carrier: A for-hire or private carrier, including its agents and the employees responsible for drivers and for inspecting and maintaining its vehicles (49 CFR 390.5).
OOS (out of service): An out-of-service order is a declaration by an authorized enforcement officer that a driver, vehicle or carrier operation may not continue (49 CFR 390.5). A vehicle marked out of service for its mechanical condition may not be driven until the required repairs are completed; it may only be towed away by crane or hoist (49 CFR 396.9).
Out-of-service criteria: The conditions, published by CVSA, under which a roadside inspector places a driver or vehicle out of service. A violation can be recorded at inspection without being an out-of-service condition.
PM (preventive maintenance): Scheduled service done before parts fail: oil and filters, lubrication, brake and tire checks, and component replacement at set intervals. The rules require systematic inspection, repair and maintenance (49 CFR 396.3) but leave the schedule to the carrier. See preventive maintenance schedules.
PM A, B, C: A common way of naming service levels, from a short, frequent service (A) to a longer, more thorough one (B, then C). The letters are a shop convention, not a regulation, and what each level includes varies from fleet to fleet.
Post-trip inspection: The driver's end-of-day check of the vehicle that produces the DVIR.
Pre-trip inspection: The driver's check before driving. Under 49 CFR 396.13 the driver must be satisfied the vehicle is in safe operating condition, review the last DVIR if one was required, and sign it to acknowledge the review and the repair certification.
Qualified inspector: A person allowed to perform the annual inspection: someone who understands the inspection criteria, has mastered the methods and tools, and has completed a federal or state training program or holds a qualifying certificate, or has at least one year of relevant training or experience (49 CFR 396.19).
Qualified motor vehicle: Under the IFTA Articles of Agreement (R245), a vehicle that carries persons or property and has two axles and over 26,000 pounds gross or registered gross weight, or three or more axles regardless of weight, or is used in a combination over 26,000 pounds. Recreational vehicles are excluded.
Recapped (retreaded) tire: A tire whose worn tread has been replaced with new tread on the original casing. A bus may not run recapped or retreaded tires on its front wheels (49 CFR 393.75).
Regrooved tire: A tire whose tread grooves have been cut deeper after wear. A bus may not run regrooved tires on its front wheels, and a regrooved tire with a load capacity of 4,920 pounds or more may not go on the front wheels of a truck or truck tractor (49 CFR 393.75). See tire tread depth.
Repair certification: The carrier's statement on a DVIR that each listed defect has been repaired, or that repair is unnecessary, made before the vehicle is driven again (49 CFR 396.11). The next driver signs to acknowledge it.
Roadside inspection: An inspection of a driver and vehicle by an enforcement officer, at a scale house, a checkpoint or the roadside. Results reach the carrier's safety record. See roadside inspections.
SMS (Safety Measurement System): FMCSA's system for ranking carriers' safety performance from inspection, crash and investigation data, organized into BASICs.
Steer tire: A tire on the front (steering) axle. On a bus, truck or truck tractor it needs at least 4/32 inch of tread depth in a major groove, against 2/32 inch for other tires (49 CFR 393.75).
Telematics: Devices and services that report a vehicle's position, distance, engine hours, idle time and fault codes from the vehicle to the office.
Tread depth: The depth of a tire's tread groove, measured in 32nds of an inch in a major groove. Federal minimums are 4/32 inch for the front tires of buses, trucks and truck tractors and 2/32 inch for others (49 CFR 393.75).
USDOT number: The identification number FMCSA assigns to a motor carrier. It appears on the carrier's vehicles and links inspections, crashes and audits to the carrier's safety record.
Vehicle Maintenance BASIC: The SMS category that counts vehicle defects found at roadside inspections, such as brakes, lights and tires. It reflects how well a carrier maintains its vehicles.
Vehicle maintenance file: The records 49 CFR 396.3 requires for each motor vehicle a carrier controls for 30 consecutive days: the vehicle's identification, the nature and due date of scheduled inspection and maintenance, and the date and nature of inspections, repairs and maintenance done. They are kept where the vehicle is housed or maintained for one year, and for six months after the vehicle leaves the carrier's control. See maintenance records.
Warranty: A maker's or seller's promise to repair or replace a vehicle or part that fails within a stated time, distance or engine hours, usually whichever comes first, and on stated conditions such as following the service schedule.
Warranty claim: A request to the warrantor to pay for a covered repair, supported by the vehicle's identity, the failure, the mileage or hours, and proof of maintenance. See fleet warranty claims.
Work order: The record of a job on a vehicle: what was wrong, who did the work, the parts and labor used, and when it was finished. Closed work orders make up most of a vehicle's maintenance history.

Fleet maintenance glossary