The purpose of the Exhaust Gas Recirculation (EGR) system is to reduce Nitrogen Oxides (NOx) emissions by lowering combustion temperatures. Lower combustion temperatures produce fewer NOx emissions. The EGR system does this by introducing inert exhaust gas into the intake. Inert exhaust gas will not combust (burn) when mixed with fuel because it does not contain oxygen. The inert exhaust gas entering the intake replaces intake air, which is rich with oxygen.

LESS OXYGEN = LESS COMBUSTION

LESS COMBUSTION = LOWER TEMPERATURE

LOWER TEMPERATURE = LESS NOx

Components and Operation

EGR valve – Located on the rear of the engine between the right side exhaust crossover tube and the EGR cooler. The EGR valve is used by the ECM to control the amount of exhaust gas that flows through the EGR cooler before it enters the intake.

NOTE: The EGR valve is cooled by engine coolant.

EGR cooler – Located on the passenger side of the engine. It uses engine coolant to cool exhaust gas, that is coming through the EGR valve, before it enters the intake. As mentioned, lower combustion temperature equals lower NOx emissions. In addition, some operating conditions produce very high exhaust gas temperatures. In these conditions, the high exhaust gas temperatures combined with the high combustion temperature could create combustion temperatures that would damage the engine.

At times, operating conditions may produce exhaust gas that is hot enough to damage the EGR cooler. If that occurs, the ECM will stop exhaust flow through the EGR valve.

EGR bypass valve – Located on the intake inlet. The ECM uses this valve to allow exhaust gas into the engine without going through the EGR cooler (EGR cooler bypass). Some operating conditions require EGR that does not go through the EGR cooler, such as at start-up (aids in warming a cold engine) or during regeneration of the Diesel Particulate Filter (DPF).

NOTE: The EGR bypass valve is cooled by engine coolant.

ECM Control

The EGR valve and the EGR bypass valve are both electronically controlled by the ECM. The ECM uses the sensors listed below, as well as others, to precisely calculate the appropriate flow and density of exhaust gas passing through either valve.

EGR temperature sensor – This sensor measures EGR gas temperature before it is mixed with intake charge air.

Exhaust gas pressure sensor – This sensor reads exhaust gas pressure from the left exhaust manifold. To maximize longevity of this sensor, it is mounted on the side of the intake manifold with a tube that connects it from the exhaust manifold to the intake manifold passage. This keeps the sensor away from high exhaust heat that could damage it.

Position sensors are located inside the EGR valves.