It could be one or more of the following components, EGR valve, EGR regulator, or a VSV (Vacum salonoid valve) which is a bit hard to reach in case you're thinking of DIY. It can also be blocked vacum hoses and carbon deposits in the intake manifold.
P0401 - EGR flow insufficient , P0402 EGR flow excessive
EGR flow insufficient.
Carbon is clogging the egr port.
The generic OBDII descriptions are EGR Flow insufficient and EGR Flow Excessive.
EGR FLOW INSUFFICIENT DETECTED.
Plugged egr tube or a failed egr valve.
P0401 = Insufficient EGR Flow
insufficient egr flow
That's your EGR valve flow is insufficient. Replace the EGR valve.
insufficient egr flow
might be the EGR VALVE insufficient flow
P0401 = Insufficient EGR Flow