#spkennyuk, thanks for your persistence with this issue.
Removed Control Module, opened casing and discovered staining and 'muck' at the bottom corner of the board around a few components and what looks like a broken track/trace (No! not the Covid track&trace...)
Tried cleaning with contact cleaner and a soft brush, which has cleaned all the cr@p away but the track/trace still looks to be damaged. Re-tried in the car but no joy.
I've ordered a PCB repair paste syringe from eBay in the vain hope I may be able to salvage the board but up to now it's looking like a replacement.
Anyone have a useable spare at reasonable cost?