2000 Mercury Sable Wagon 3.0L Vulcan "U" motor. Vehicle set check engine light code P1405 was able to clear code but checked under hood found what I believe is the DPFE sensor burned through at the electrical connection and one plastic nipple melted, one hanging loose, one hose still connected. What caused this melting of the sensor is it old age a misfire or some other fault? If I replace the damaged parts will this happen again? This is the first mercury I have owned and am not really familiar with the drivetrain. At present no codes, vehicle seems to drive ok.