Answer: Since 1975, every vehicle produced in the United States is required to have a catalytic converter. A catalytic converter is responsible for controlling harmful emissions from your vehicle. It is located on the bottom of your vehicle, just behind your engine. Breaking down its name, we can analyze exactly what its function is. Catalytic converters contain substances or compounds such as platinum, rhodium, or palladium that act as catalysts and converters. The compounds act like catalysts because they cause a chemical reaction to occur, but they don’t change their original form. The compounds also act as converters because they react with and convert harmful gases such as carbon monoxide, hydrocarbons, and nitrogen oxides produced by your engine. This conversion into less harmful gases occurs before they travel out your exhaust system and into the air. Catalytic converters contain honeycomb (covered with tiny pores) structures that are coated with platinum, rhodium, or palladium depending on the catalyst stage. Exhaust emissions from the engine will travel through the coated honeycomb structures and react with the compounds. There are two different catalyst stages that emissions will travel through: a reduction catalyst and an oxidation catalyst. During the first catalyst stage (the reduction catalyst), nitrogen oxides react with a platinum and rhodium coated honeycomb structure. When these harmful nitrogen oxides react with the catalysts (platinum and rhodium), the catalysts remove the nitrogen molecule, hold onto it, and release the oxygen molecules. Then, the nitrogen molecules left over will join with other nitrogen molecules and exit through the exhaust system. During this stage, harmful nitrogen oxide gases are converted into harmless oxygen and nitrogen gases. During the second catalyst stage (the oxidation catalyst), carbon monoxide and hydrocarbons are oxidized. This means that oxygen molecules will react with the carbon monoxide and hydrocarbon molecules. These substances pass through a platinum and palladium coated honeycomb structure, which acts as a catalyst and aids in the reaction. During this stage, very harmful carbon monoxide and hydrocarbon gases are converted into less harmful carbon dioxide gases and water vapors. Catalytic converters also work hand-in-hand with a control system. This control system controls the fuel injection system and monitors the emissions leaving the engine before they enter the catalytic converter. It also contains an oxygen sensor, which detects how much oxygen is entering the exhaust system. The oxygen sensor monitors the amount of oxygen and will tell the fuel injection system to increase or decrease the amount of oxygen used in the fuel/air mixture used to power the engine. The sensor also makes sure there is enough oxygen in the exhaust system to be used by the catalytic converter in the oxidation catalyst stage.