Emissions systems are components of a vehicle's exhaust system that are designed to reduce the amount of harmful pollutants released into the atmosphere. These systems typically include a catalytic converter, an oxygen sensor, and an exhaust gas recirculation (EGR) valve. The catalytic converter helps to reduce the amount of carbon monoxide, hydrocarbons, and nitrogen oxides released into the atmosphere. The oxygen sensor monitors the amount of oxygen in the exhaust and adjusts the fuel-air mixture to ensure the most efficient combustion. The EGR valve helps to reduce the amount of nitrogen oxides released into the atmosphere by recirculating some of the exhaust gases back into the engine.