alrite my check engine light came on today, and its the po402 code. the code description is eccesive egr floe. now does that warrent a new egr valve, or a dpfe sensor?
In my experience the DPFE is at fault slightly more often than the EGR valve itself. This could also be the vacuum lines to/from the DPFE as well.
I have replaced a lot a good EGR valves trying to diagnose problems like this.
Suggest starting with the vacuum lines to/from the DPFE. Any leaks in these lines could cause a false DTC. If you replace the lines, remember that they carry exhaust gasses. Regular vacuum lines can be used but they will not give long service life. Also note, the lines are different sizes. There is a replacement kit from Ford. They are somewhat $$ for what they are. Also, they are difficult to replace because of interference from the firewall.
Check the EGR tube itself. Look for any exhaust leaks as this could cause a false DTC.
To further nail this down, disconnect and plug the vacuum line to the EGR valve itself. If the code stays, then the problem is in the EGR valve.
Of course if this is a high mileage car, it is not a bad idea to start with the EGR valve. Clean the Throttle body EGR passages as well. They will sometimes become blocked with carbon deposits.
Note: Ford has updated the design of the DPFE to reduce the number of false positives. Should you replace the DPFE, consider getting directly from Ford. This will give you the latest version.
>>>from Ford CD P0402 - EGR Flow Excessive Detected
The EGR system is monitored for undesired EGR flow during idle. The EGR monitor looks at the DPF EGR signal at idle and compares it to the stored signal measured during key ON and engine OFF. The test fails when the signal at idle is greater than at key ON engine OFF by a calibrated amount.