2015 Citroen Berlingo non start- earth problems

After some advice please, have a Berlingo van. When you try to start there is no ignition lights, but 12v across the battery (new battery). When you link the neg batt terminal to the jump start point on the body, you get ignition lightd and the van attempts to start but only clicks once, you then put a jump pack on the battery poss and jump start point and it fires up. Once running with my multi meter i get 12v across the battery terminals, but if i earth out on the body i get the desired 14.4v. I have accessed the start stop module behind the N/S/F wing. The one earth off the battery goes to this, which then supplies the body earth. Is it common for these to ECUs to fail and if they do, do they tend to require the the condensor as well? Also are these plug and play or do they need programming? If i get the right answer hear, it will be a first, because even my local Citroen garages cant tell.