I recieved a P401 code. Had this same problem about 10K miles ago. Took it to the dealer and they fixed it. DPFE sensor and cleaning....

Now it came back.

Took the upper intake off. Found one of the EGR ports clogged, so gave the throttle body and plenum a good cleaning.

Put everything back together. I even replaced most of the rubber vacumn hoses and put clamps on all of them. Just in case....

Code came back.

Now I go and get a new EGR.

Took longer to get the CEL but it DID come back.

The only thing I have not done is:

1. Replace the DPFE sensor
2. Check/clean the two exhaust lines to the DPFE sensor
3. Replace the DPFE sensor switch.

Not real sure what to do next.

I guess the easiest is to clean those two exhaust lines running to the DPFE sensor.

Any more suggestions?

 

Just had the same thing last month. Replaced DPFE and all is well.