Glossary

A

ABS (Anti-Lock Braking System)
A safety system that prevents wheels from locking up during hard braking.

Air Brake System
A braking system that uses compressed air instead of hydraulic fluid.

Air Dryer
A device that removes moisture from compressed air in brake systems.

Alignment
Adjustment of wheels so they are parallel and properly angled for safe driving and tire wear.

Alternator
Charges the battery and powers the electrical system when the engine is running.

APU (Auxiliary Power Unit)
A small engine that powers cab accessories without idling the main engine.

B

Blow-By
Excess gas escaping from engine cylinders into the crankcase due to worn piston rings.

Boost Pressure
Compressed air created by the turbocharger to increase engine power.

Brake Chamber
Converts air pressure into mechanical force to apply brakes.

Brake Slack Adjuster
Controls the distance between brake shoes and drums.

C

Cab-Over Engine (COE)
Truck design where the cab sits over the engine.

Camshaft
Controls valve opening and closing inside the engine.

Carrier Bearing
Supports the driveshaft on long vehicles.

Clutch
Connects and disconnects engine power to the transmission.

Coolant
Fluid used to control engine temperature.

Crankshaft
Transforms piston motion into rotational engine power.

D

DEF (Diesel Exhaust Fluid)
Fluid used to reduce emissions in modern diesel engines.

Differential
Allows wheels to rotate at different speeds while turning.

Diagnostic Scan Tool
Electronic device used to read engine fault codes.

DPF (Diesel Particulate Filter)
Traps soot in diesel exhaust systems.

Driveline
All parts that transfer engine power to the wheels.

E

ECM (Engine Control Module)
The computer that controls engine operations.

EGR (Exhaust Gas Recirculation)
Reduces emissions by recirculating exhaust into the engine.

Exhaust Back Pressure
Restriction in exhaust flow that reduces engine performance.

F

Fifth Wheel
Coupling device connecting the truck to the trailer.

Fuel Injector
Sprays fuel into the engine combustion chamber.

Fuel Rail
Delivers fuel to the injectors under high pressure.

Flywheel
Stores rotational energy and helps start the engine.

G

Gear Ratio
Relationship between drive gears affecting speed and torque.

Glow Plug
Heats air in diesel engines for cold starts.

GVWR (Gross Vehicle Weight Rating)
Maximum safe weight of a vehicle including cargo.

H

Hydraulic System
Uses pressurized fluid to operate mechanical components.

Horsepower
Measurement of engine power output.

I

Idling
Running the engine while the vehicle is stationary.

Injector Balance Rate
Measurement of fuel delivery accuracy between injectors.

J

Jake Brake (Engine Brake)
Uses engine compression to slow the truck.

K

Kingpin
Vertical pin connecting trailer to the fifth wheel.

L

Lift Gate
Hydraulic platform used to load and unload cargo.

Low Air Warning
Safety alert when air brake pressure becomes too low.

M

Mobile Repair Service
On-site truck repair performed roadside.

Misfire
When fuel fails to ignite inside a cylinder.

MPG (Miles Per Gallon)
Fuel efficiency measurement.

N

No-Start Condition
When a truck fails to start due to electrical, fuel, or mechanical issues.

O

Oil Cooler
Keeps engine oil temperature regulated.

Overhaul
Complete rebuilding of an engine or major system.

P

PTO (Power Take-Off)
Transfers engine power to auxiliary equipment.

Preventive Maintenance
Routine servicing to avoid major breakdowns.

Purge Valve
Releases moisture from air dryer systems.

Q

Quick Disconnect Fittings
Connectors allowing fast air or fluid line removal.

R

Radiator
Cools engine coolant using airflow.

Reefer Unit
Refrigeration system on temperature-controlled trailers.

Regeneration (Regen)
Burning soot from the DPF filter.

S

Starter Motor
Cranks the engine to start it.

Slack Adjuster
Sets brake clearance automatically or manually.

Suspension System
Supports vehicle weight and absorbs road shock.

T

Tandem Axle
Two axles positioned close together for added weight capacity.

Thermostat
Controls engine coolant flow.

Turbocharger
Uses exhaust gases to boost engine power.

Transmission
Transfers engine power to wheels.

U

U-Joint (Universal Joint)
Allows driveshaft movement while rotating.

V

Valve Lash
Clearance between valve components for proper engine operation.

Vehicle Diagnostics
Electronic testing of engine and control systems.

W

Wheel End
Assembly that includes hub, bearings, seals, and brake components.

Wheel Speed Sensor
Measures wheel rotation for ABS systems.

X

X-Pattern Torque
Bolt tightening pattern for even pressure distribution.

Y

Yaw Stability Control
Electronic stability system to prevent rollovers.

Z

Zerk Fitting
Grease fitting for lubricating moving parts.