I have a 2002 Mercury Sable and the check engine light is on and when i pulled the code on it. It came up as a P1400 saying that there is low circuit voltage i replaced the DPFE do anyone have any suggestions?

 

if you just replaced it, give it 4 full temp cycles to adjust. If the code still doesn't go away, then there may be a wiring issue (broken wire, bad contact) that needs to be fixed. check the wire harness that goes to the DPFE and make sure it's clean. then follow the wires and make sure something hasn't damaged them if you can.