1993 Honda Civic Owner's Manual - Page 180

Emission Controls The burning of gasoline in your car's engine produces several byproducts. Some of these are carbon monoxide (CO), oxides of nitrogen (NOx), and hydrocarbons (HC). Gasoline evaporating from the tank also produces hydrocarbons. Controlling the production of NOx, CO, and HC is important to the environment. Under certain conditions of sunlight and climate, NOx and HC react to form photochemical "smog." Carbon monoxide does not contribute to smog creation, but it is a poisonous gas. The Clean Air Act The Clean Air Act* sets standards for automobile emissions. It also requires that automobile manufacturers explain to owners how their emission controls work and what to do to maintain them. This section summarizes how the emission controls work. Scheduled maintenance is on page 104. * In Canada, Honda vehicles comply with the Canadian Motor Vehicle Safety Standards (CMVSS) for Emissions valid at the time they are manufactured. Crankcase Emission Control System Your car has a Positive Crankcase Ventilation (PCV) System. This keeps gasses that build up in the engine's crankcase from going into the atmosphere. The PCV valve routes them from the crankcase back to the intake manifold. They are then drawn into the engine and burned. Evaporative Emission Control System As fuel evaporates in the fuel tank, an evaporative emission control canister filled with charcoal adsorbs the vapor. It is stored in this canister while the engine is off. After the engine is started and warmed up, the vapor is drawn into the engine and burned during driving. Technical Information