Exhaust Gas Recirculation (EGR) Cooling System

The EGR cooling system is provided with two temperature sensors that measure the temperature of the exhaust gas at the inlet and outlet of the EGR cooler. The ECM supplies 5 volts to the EGR temperature sensor signal circuit and a ground for the low reference circuit. When the EGR temperature sensor is cold, the sensor resistance is high and when the EGR temperature increases, the sensor resistance decreases.

The system also contains an exhaust gas cooler which is provided with a bypass valve. Integral tubes in the EGR cooler core help carry away excessive exhaust gas heat. Engine coolant flows through the cooler to help cool the exhaust gases flowing to the EGR valve. The cooler must remain within a specific temperature range to efficiently reduce emissions. The ECM determines the efficiency of the cooler by monitoring both EGR temperature sensors while the EGR valve is active. If the difference between the EGR cooler temperature sensors exceeds a calibrated threshold, this diagnostic will fail and a DTC will set.

The EGR cooler bypass solenoid valve is controlled by the ECM. At engine cold start, the cooler bypass valve allows hot exhaust gas to heat the intake air in the manifold to reduce emissions. Once the engine operating temperature is reached, the ECM will close the valve, to allow exhaust gas to flow through the EGR cooler. During Idle and light load operations, the valve is opened, to allow the exhaust gas to bypass the cooler and prevent fouling of the cooler passages.