​When the EGR valve is open, some of the gas coming out of the exhaust manifold is sent back to the combustion chamber with the help of EGR. In this way, the oxygen rate in the interior is reduced, which significantly reduces the combustion temperature. At low combustion temperatures, NOx gases cannot be formed as much as before, thus reducing emissions. When the engine is fully loaded, the EGR valve is closed by the engine computer and stops sending exhaust gas to the combustion chamber, as performance is required from the vehicle. In this way, the combustion chamber, which is completely filled with oxygen, produces more power. The EGR valve may become contaminated due to the exhaust gases passing through it and a blockage may occur in it. The EGR system should be cleaned regularly in terms of factors such as soot, time and rust that cause EGR malfunctions. It is time to clean an EGR system; If dark black smoke comes out of the exhaust pipe, the engine stutters or does not start, the engine temperature rises, if it persists, the engine is damaged, fuel consumption increases rapidly, if there is a misfire caused by the gas pedal, the symptoms indicate that it is time to clean.