replace your dpfe and clean out all your egr passages. don't drop the 60 bucks on a valve until you've tried these other options. the clogged passages might require removing your throttle body and cleaning the c-shaped port there, but i am not totally familliar with your engine.
good luck.
mb
Trouble code P0401 means:Exhaust gas recirculation flow insufficient detected
Exhaust gas recirculation insufficient flow detected
Trouble code P0401 means:Exhaust gas recirculation flow insufficient detected
Trouble code P0401 means: Exhaust Gas Recirculation Malfunction
Trouble code P0401 means: Exhaust Gas Recirculation Flow Insufficient Detected
Trouble code P0401 means:Exhaust gas recirculation-insufficient flow detected
P0401 = Insufficient EGR Flow
The generic OBDII descriptions are EGR Flow insufficient and EGR Flow Excessive.
Trouble code P0401 means:Exhaust gas recirculation flow insufficient detected
2.0L perhaps? p0351= intergrated ignition coil failure (possible # 1 coil failure or short, start/run circuit issue, bad PCM p0401= EGR (flow problem),valve problem, solenoid problem, possible hoses, maybe even the PCM
Trouble code P0401 means: Exhaust Gas Recirculation Malfunction
P0401 = Insufficient EGR Flow