This video explains how the complete exhaust gas recirculation system functions. The egr cooler helps to reduce exhaust gas temperatures before they are administered back into the combustion. The by-pass valve sends hot air to reduce condensation. The EGR Valve will only open when prompted by the ECU. This will help to cool the combustion chamber subsequently reducing the formation of Nitrogen oxides, Nitrogen dioxide or Nitrogen monoxide. The EGR position sensor is a Hall-effect sensor. The EGR Valve servo motor turns in both directions but some of them are closed by spring pressure. High temperatures in the combustion chamber can be a catalyst in the formation of oxides of nitrogen especially above 2000 degrees Celsius.