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.

Glazing is a shiny coating on the inside surface of a fan, or serpentine belt. Glazing occurs when the belt slips repeatedly at a high speed. It is a sign that the belt needs replacement.

Glow plugs are only found on vehicles with diesel engines. Glow plugs heat up the diesel fuel before the engine has been started, making the engine easier to start.

The hazard relay controls the flashing of the hazard warning lights.

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

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.

A gauge is a type of instrument that measures or displays levels of a certain system. For instance, the gas gauge in your car measures the fuel level, while the temperature gauge measures the engine temperature.

The gear selector is the lever that lets you select a certain gear with an automatic transmission. In modern cars, the gear selector is often connected to the brake pedal, so that you can only shift into drive or reverse

Gear synchronizers allow you to upshift and downshift a manual transmission without grinding gears. They do this by synchronizing, or matching, the speed of the engine and the speed of the gear you are selecting. If your car didn’t have

The gearshift lever is the lever that lets you select gears with a manual transmission.

This is a series of rods and/or cables that connect the gearshift lever or gear selector to the transmission.