egr flow insufficient

For this particular DTC it can be a PIA to track down. About equally it can be the DPFE, Clogged/rotted EGR valve, the vacuum lines to/from the DPFE.

Since you have already bought a DPFE, recommend inspection of the vacuum lines to/from the DPFE. Any leaks can cause this DTC.

The post does not state the mileage of the car. If high mileage, this could be caused by carbon build up blocking the EGR flow through the throttle body. Consider cleaning the throttle body EGR passage ways.

Also, if high mileage, the EGR valve itself could be bad. If if were my car and 100K plus miles, I would replace it at the same time I cleaned the throttle body.

mine had a broken vacuum line at the egr valve