Is there a sensor for insufficient air flow?

My guess you are saying its a P0401 EGR flow code. If it is its nmot likely a bad sensor. Most likely the EGR passages in the intake manifold are stopped up with carbon.

This code comes on when carbon builds to the point of being a solid crystal, it's needs to be drilled completely out clear all passages to allow air flow again. Preventative in future would recd. fuel system services every 20-30k