Sensor - EGR Back Pressure: Operation
WARNING: This page is about a different car, the 2006 Dodge Magnum, 2006 Dodge Charger, and 2006 Chrysler 300. However, it is still accessible from the selected car via links, so may be relevant.
The exhaust gas effects a sensor membrane that acts against a potentiometer internal to the sensor. The potentiometer changes the resistance value and thus influences the signal voltage of the sensor.