An acronym for Hydrocarbons. Any number of compounds of carbon and hydrogen used as fuel, such as gasoline. High levels of hydrocarbons in tailpipe emissions are a result of unburned gasoline.

The head gasket seals the cylinder head to the engine block. It is subject to tremendous pressures, and often fails if and when an engine overheats.

The heater core is a miniature radiator that sits in the dashboard. When the heater is turned on, it opens the heater valve which lets hot coolant into the heater core, which then warms the air coming into the vehicle’s

The heater ducts are the tubes that connect the heater fan to the vents in your vehicle’s dashboard.

The heater fan is the interior fan that controls the speed of air being introduced into the interior.

The heating system warms the air brought into a vehicle’s interior. The heating system is connected to the cooling system and consists primarily of the heater core, heater valve, and, if equipped, a climate-control system.

The heater valve is controlled by the interior heating controls. When you turn on your vehicle’s heat, the valve opens and allows hot coolant to enter the heater core, which then warms the air entering your vehicle’s interior.

Hub is a generic term for the area where a wheel is mounted. For instance, there are hubs for every wheel on your car.

HVAC is a mechanic’s term for your car’s ventilation system. The letters stand for Heating, Ventilation, and Air-Conditioning.

The hydraulic circuit is a closed system of tubes that contain hydraulic fluid. When pressure is applied at one end of the hydraulic circuit, it travels through the tubes to the other end.

A generator is like an alternator in that it generates electrical current to both keep the battery charged and supply electricity for a vehicle’s electric system.

Fuel injection is a system by which fuel is directly sprayed into the intake manifold or intake port at high pressure. Fuel injection is often controlled by a computer, allowing precise monitoring of efficiency and performance by the car’s computer.

A fuel injector is a nozzle that sprays fuel into the intake manifold or intake port.

The fuel pump moves gas from the gas tank and delivers it to the fuel injection system or carburetor.

Fuel starvation occurs when fuel, for one reason or another, is prevented from reaching the carburetor or fuel injectors.

The fuel system is the system by which fuel is stored and delivered to each cylinder. The fuel system includes the fuel tank, fuel tank level sending unit, the fuel pump, the fuel filter, and fuel lines. For carbureted cars,

This unit measures the amount of gas in the fuel tank and sends that information to your vehicle’s gas gauge and, if equipped, a low gas level warning light.

Front-wheel drive (FWD). A front-wheel drive vehicle sends its power to the front wheels of the car.

This is a general term that refers to a gasoline’s general quality – for instance, its octane rating and package of additives. The two common terms for gas grades are “regular” for low-grade gas, and “premium” for high-grade gas.

A gasket is a piece of material that seals two parts together. The gasket prevents air or fluids from leaking between the parts.