| Description and Operation Positive Crankcase Ventilation System The positive crankcase ventilation system consists of a valve and several hoses. The positive crankcase ventilation system recycles crankcase gases back through the engine where they mix with the incoming air/fuel charge. The positive crankcase ventilation valve regulates the amount of ventilation air and crankcase gas supplied to the intake manifold and also prevents backfiring into the crankcase. The positive crankcase ventilation system helps to reduce hydrocarbon emissions from the engine. Exhaust Gas Recirculation System The exhaust gas recirculation system consists of a valve, a vacuum regulator valve, a tube and a differential pressure sensor. The exhaust gas recirculation system recycles measured quantities of exhaust gas back through the engine where they mix with the incoming air/fuel charge. The powertrain control module controls the vacuum regulator valve with grounding pulses. This regulates the amount and duration of the vacuum signal supplied to the exhaust gas recirculation valve and thus the valve lift and opening time are controlled. The differential pressure sensor provides the powertrain control module with data relating to the exact amount of exhaust gas being recirculated by measuring the differential pressure across a calibrated orifice in the supply hose. Thus, closed loop control is achieved. | 
