The EGR (Exhaust Gas Recirculation Valve) is part of the vehicle emissions system. Its function is to reduce the combustion temperature, as well as the pressure to control the NO (Nitrogen Oxides).
In general, this system has three parts which are: The EGR valve, a solenoid drive and a Differential Pressure Feedback Sensor (DPEF). All these components work together to deliver the amount of recirculation that is needed. This delivery is based on the temperature and the load of the motor. When the fault code P0401 OBD2 is established, it indicates that the amount of recirculation has been detected to be insufficient.