The code PO405 is set when DPFE sensor signal voltage is less than 0.2v. To test, use scan tool to check the DPFE sensor voltage. It should read roughly 1.0v Key On Engine Off. If you don't have a scan tool use a volt meter to check the voltage on the Brown/lite green wire at the DPFE sensor with the sensor connected.If the voltage is less then 0.4v, disconnect it and the voltage should go to 5v. If it dose, replace it because it shorted and this is very common. Let me if I can assist.