So... About the EGR system. What's the theory behind the Backpressure Transducer (BPT) Valve? I know what it does... It disables the EGR system if the exhaust backpressure is too low. Question is "Why?" What would be wrong with having the EGR enabled even when the exhaust backpressure is low? Seems to me that it would simply recirculate less gas under low exhaust pressure conditions. Is there really a need to disable it completely under those conditions?