Plain-English definitions for the terms mechanics, fleet managers, shop owners and parts vendors use every day.
ABS— Anti-lock Braking System
A safety system that prevents wheels from locking up during hard braking by rapidly modulating brake pressure, helping the driver retain steering control.
Alternator— Electrical generator
A belt-driven generator that converts mechanical engine power into electricity to charge the battery and run the vehicle's electrical loads while the engine runs.
Catalytic Converter— Emissions control
An exhaust component that uses precious-metal catalysts to convert harmful pollutants (CO, NOx, HC) into less harmful gases before they exit the tailpipe.
CVT— Continuously Variable Transmission
A transmission with no fixed gears that uses a belt and variable pulleys to provide a seamless range of effective gear ratios.
DEF— Diesel Exhaust Fluid
A urea-water solution injected into the exhaust of modern diesels (SCR systems) to chemically reduce NOx emissions. Empty or contaminated DEF will derate the engine.
Differential— Drive axle gearbox
A gear assembly in the drive axle that splits engine torque between two wheels while allowing them to spin at different speeds when turning.
DOT— U.S. Department of Transportation
Federal agency that regulates commercial vehicles, drivers, and motor carriers in the United States, including inspections, hours of service, and CDL requirements.
DPF— Diesel Particulate Filter
An exhaust filter on diesel engines that traps soot. It periodically performs a 'regen' to burn off captured soot, which can be active, passive, or forced.
ECM/ECU— Engine Control Module / Unit
The vehicle's primary engine computer. It reads sensor inputs and controls fuel injection, ignition timing, emissions systems, and many other engine functions.
EGR— Exhaust Gas Recirculation
An emissions system that routes a metered amount of exhaust gas back into the intake to lower combustion temperatures and reduce NOx output.
Flat Rate— Pay/billing model
A pricing and pay model where each repair job is assigned a fixed labor time (e.g. 1.5 hours), regardless of how long the technician actually takes.
FMCSA— Federal Motor Carrier Safety Administration
U.S. agency within the DOT responsible for regulating and enforcing safety rules for commercial motor vehicles and their drivers.
Labor Rate— Hourly shop rate
The dollar amount per hour a repair shop charges customers for labor. Differs from technician wage; the shop's rate covers overhead, profit and benefits.
OBD-II— On-Board Diagnostics II
The standardized vehicle diagnostic system required on light-duty vehicles sold in the U.S. since 1996, accessed via a 16-pin port and producing DTC fault codes.
OEM— Original Equipment Manufacturer
Parts made by the same manufacturer (or their contracted supplier) that produced the original part installed at the factory. Contrast with aftermarket parts.
Preventive Maintenance (PM)— Scheduled servicing
Routine, scheduled service intended to prevent failures and extend vehicle life, including oil changes, filters, inspections, and component replacements.
Starter— Engine starting motor
An electric motor that engages the engine's flywheel to crank the engine until combustion takes over and the engine runs on its own.
Telematics— Fleet vehicle data
Onboard hardware and software that captures and transmits vehicle data — location, speed, fuel, diagnostics, driver behavior — usually for fleet management.
Transmission— Gearbox
The component that multiplies engine torque and selects gear ratios to match the vehicle's speed and load. Types include manual, automatic, CVT, and DCT.
Turbocharger— Forced induction
An exhaust-driven turbine that compresses intake air, allowing the engine to burn more fuel and produce more power for its displacement.
Work Order— Shop repair document
The internal shop document that authorizes, tracks, and bills a vehicle repair. Includes customer info, vehicle, complaint, cause, correction, parts, labor and totals.