High Pressure EGR Operation:

During cold engine conditions (coolant temperature under 55°C (131°F)) all EGR flow comes from the high pressure EGR system. This is due to the lower pressure and temperature in the low pressure EGR system which may lead to condensation. The high pressure EGR system pulls exhaust gases from the exhaust manifold. The exhaust gases flow through the a cooler to the intake manifold. During cold start conditions, the EGR bypass valve is opened and the exhaust gases are diverted around the cooler through the bypass pipe. The advantage is that the exhaust gas temperature and pressure is higher which can warm the engine quickly. The disadvantage of the high pressure EGR is that the exhaust gases have more soot which can eventually lead to coking in the engine. The EGR temperature sensor is located in the path between the EGR cooler and EGR valve. The Powertrain Control Module (PCM) monitors the temperature sensor signal to determine flow of the system based on commanded EGR valve position.

The Powertrain Control Module (PCM) calculates the flow rate of the high pressure EGR system and compares it to the commanded EGR flow rate. In order to calculate the high pressure EGR flow rate the PCM monitors the input signals from the boost pressure sensor, EGR temperature sensor and intake air temperature sensor. If the PCM determines that the high pressure EGR cannot produce enough flow it will commanded the EGR airflow control valve partially closed to increase EGR flow.