The exhaust-gas recirculation (EGR) system is designed to introduce exhaust gas into the engine’s intake manifold. Up to a certain degree, this system enables to reduce the formation of oxides of nitrogen (NOx) by cooling the combustion process. EGR solenoid valve(A) will not open under all driving conditions. For it to cycle, the engine must be at normal operating temperature and not under heavy load. The amount and timing of exhaust gas introduced into the combustion cycle varies by such factors as engine vacuum, exhaust system back pressure, coolant temperature and accel position. Depending upon the engine’s operating point, the air/gas mass drawn into the cylinders can be composed of up to 40% exhaust gas. Using the signal generated by the ECM control circuit, the EGR valve opens so that exhaust gas can flow into the intake manifold. If the EGR valve begins to clog or only partially opens, its flow will be reduced and emissions will increase.