The design of the Exhaust Gas Recirculation (EGR) system has the objective of minimizing the combustion temperatures, allowing the emission of nitrogen oxides to be low. To do this, it sends the cylinder back to the inert exhaust gases in order to be burned with the air-fuel mixture. In this way, the inert exhaust gas burns slower.
The valve of the EGR system is controlled by the PCM (Power Train Control Module). This valve opens to let the exhaust gases flow to the cylinders.
Depending on the model, the valve can be controlled by vacuum. In this case, there is a vacuum solenoid that is controlled equally by the PCM. There are also EGR valves that are electronically controlled directly by the Powertrain Control Module (PCM).
The EGR system also has a feedback sensor known as an EVP sensor (EGR valve Position Sensor) which is responsible for informing the computer of the actual position of the EGR. The normal sensor voltage is 0.4 to 5 volts. If the EVP sensor gives a reading that is excessive for a long time, the DTC code P0406 OBD2 is set.