H

Heated Air Inlet System:

HEATED AIR INLET SYSTEM - System which operates during cold weather and cold start. Its purpose is to bring warm, filtered air into the engine to control the volume of air entering the engine, vaporize the fuel better and reduce HC and CO emissions.

Heated Exhaust Gas Oxygen Sensor:

HEATED EXHAUST GAS OXYGEN SENSOR (HEGO) - EGO Sensor with a heating element.
HEAT STOVE - Shroud placed over the exhaust manifold to trap heat. Ambient air is drawn between the shroud and manifold to heat it during cold ambient or cold engine conditions.

HIGH FREQUENCY OSCILLATIONS The short-tracing vertical image lines which are seen between its lowest point, up and back down to the beginning of the dwell.
HOT AIR TUBE - Tube, often made of treated paper (on older cars it is made of metal) which conducts hot air from the manifold heat stove to the air cleaner.
HOT SOAK - Period of time after an engine operates where excess heat dissipates from the engine.

HYDROCARBON (HC) - A chemical composition made up of hydrogen and carbon, such as petroleum.

HYDROGEN - Highly flammable elemental gas. Chemical symbol is H.