H
Haldex clutch
Limited slip coupling used in vehicles with automatic all-wheel drive systems to engage and disengage a secondary axle when needed.
HCCI
Homogeneous charge compression ignition. An internal combustion engine in which gasoline and air are compressed to the point of auto-ignition.
Head room
The distance from the hip of a vehicle's occupant to the vehicle's interior rooftop.
Head unit
The central control unit for a vehicle's entertainment system.
Headlight washers
A set of washer nozzles and/or wipers that clean a vehicle's headlights.
Headlights
A pair of bright lamps that provide visibility during darkness.
Headsets
A pair of small speakers that, when placed close to a passenger's ears, enables the passenger to listen to a vehicle's sound system without disturbing other passengers.
Heads-up display
A digital display projected from a vehicle's dashboard onto its windshield to provide information within the driver's direct line of sight.
 
 
Heated air temperature sensor
A device that provides information needed by a vehicle's computer to determine the temperature of the air coming into the engine.
Heated mirrors
Sideview mirrors with internal electronic heating coils designed to prevent fog and ice from obstructing visibility.
Heater
A heat exchanger placed in the ventilation system that diffuses heat from the engine's cooling system into an airstream generated by an inline fan.
Heater hoses
Tubing that carries engine coolant between a vehicle's cooling system and heater core.
Height
The distance between the tallest part of a vehicle and level ground.
Highway fuel economy
The average number of miles a vehicle is able to travel using one gallon of fuel according to EPA simulated laboratory tests of highway driving conditions.
Hill holder
A device that applies brake pressure when a vehicle's clutch is disengaged.
Hinge type
The type of door hinge: standard, scissor, gullwing or suicide-style.
Hip room
The distance from the driver's side lower door panel to the front passenger's lower side door panel.
 
 
HVAC
Heating, ventilation and air conditioning.
Hybrid degree
The level of hybrid technology used for a vehicle: full, mild, power-assist or plug-in.
Hybrid drivetrain layout
The drivetrain layout in a hybrid vehicle: parallel, series or combined.
Hybrid engine
A powertrain that combines an electric motor and an alternative means of propulsion and/or power generation (for example, hydrogen). A gas/electric hybrid engine is the most common example of a hybrid engine.
Hybrid gas engine performance
A hybrid vehicle's gasoline engine's ability to do work, expressed in terms of horsepower or torque.
Hybrid performance
A hybrid engine and electric motor's combined ability to do work in terms of horsepower, torque or efficiency.
Hybrid power source
The source of power in a hybrid vehicle: gas/electric, plug-in, fuel cell or pneumatic.
Hybrid vehicle
A vehicle that combines the use of internal combustion and electricity as power sources.
Hydrocarbons
Organic compounds commonly used as a fuel source consisting of only hydrogen and carbon atoms.
Hydrogen fuel cell
An energy conversion device that produces electricity by means of electrochemical reactions between hydrogen and an oxidant.