PO401 OBD-II trouble code

HI
2000 ranger 3.0 v6, last year engine light came on. Advance auto did code check PO401. Removed EGR valve and tube found no carbon buildup or clog so i replaced DPFE sensor and no problem for 8 or 9 months. Engine light is back on with the same PO401 code. Could use some advice on what to do next.
Thanks

Need to take off the throttle body, and clean both the throttle body, and EGR gase
passages. The Emission gunk will plug your Egr passages, and contaminate your throttle body.
Also see http://www.ideabuyer.com/ipavail/acme-auto-emissions-filter

I'd replace the EGR valve. PO401 is insufficient flow EGR Valve. If the passages in the throttle body were plugged up the computer would sense insufficient flow and would over compensate by PO 402 Excessive flow EGR valve. I had this happen on my Escort. Replaced the EGR. Everything is fine now.

There are many possibilities here.
1st check vacuum lines to ERG from EGR solenoid and then to manifold vacuum. Look for holes cracks or loose fittings.
2nd check hoses to DPFE valve.
3rd clean EGR tube
4th check flow thro DPFE and solenoid use manual to see how
5th check the solenoid for continuity
6th pull vac line from EGR while idling engine should stall. If not consider replacing 1 egr control solenoid 2 DPFE sensor 3 egr valve itself.

It took me 2 years to find out the check engine cause was the EGR solenoid