Ive experimented around with bypassing my EGR system. Ive tryed plugging the vacume hose, and I once made a plate to block the passage. I recieved check engine lights both times very soon after. I imagined the EGR temp sensor wasnt reading any temp due to the blockage and sent me a code. To the best of my knowledge, the EGR temp sensor is the only thing that can really give you a code 71. So if your getting vacume to your EGR and the diaphram is opening, Id look at the sensor circuit.