Intermittent EGR probelms

[Normie]

Hi everyone. Experiencing intermittent problems with the EGR system on my 2015 Insignia 1.6 CDTI.  Problem occurs randomly - anywhere between 25 and 500 miles of driving. EM light comes on and OBD reader shows Fault Code P0401 - Exhaust Gas Re-circulation Insufficient. At no time do I sense any drop in power etc. I normally pull over, clear the fault code and then drive on until the next episode.

I am confident it is not the actually EGR valve, having now fitted a second replacement.

Questions for members:-

a) have any other owners experienced similar problems - and how were they resolved 

b) any information on the 'number of' and 'function of' the various sensors involved in controlling the EGR valve would be much appreciated

Thanking you all in advance

regards.