The sensor measures temperature of the EGR . It sends a signal to the ECU that the Temperature is in the correct range. It serves no other purpose then to report. If you have a engine code 71 a 10k ohm resistor into the the plug will fool the ECU that the EGR is within normal parameters.
The EGR functions as a fire extinguisher to cool the engine temperatures while in certain engines modes ( coasting ) During start up or WOT the system is suppose to be closed.