Just to follow up n this. I found the pdc ecu located above the cd changer in the boot (behind the carpet). All the wiring looked intact and no signs of water ingress.
So I proceeded to loosen the bumper, just the left hand screws (4 in the wheel arch), the 2 torx screws under the bumper, and popped out the light fitting, and the torx bolt there.
I then had enough room to get at the outer most sensor (MES flagged it as the culprit) swapped sensor with a used one from eBay, put everything back together and happy days, I have working sensors again!
2015 - Today 159 2.4 JTDm
2012 - Today GTV 3.0 V6 24v
Gone by not forgotten!
2013 - 2015 156 SW 2.4 JTD
2013 - 2013 145 QV Shed for 1 week - RIP
2011 - 2012 Brera S 3.2 V6 number 21/178
2007 - 2011 GTV 3.0 V6 Q2