Hi Simon,
Where are you based? On the cars with this issue we have seen water ingress into the BCM in the driver footwell or into the IPDM unit under the scuttle panel in the engine bay.
I would take a look under the bonnet at the IPDM unit. It's on the passenger side under the scuttle panel the there is a rubber one way grommet (as a water drain) underneath the unit. Chances are yours is dislodged and you have had a load of water come through the hole. Look for green discolouration on contacts as that's where the water has been.
If it's not that then look at the BCM in the drivers footwell, again looking for signs of water.
Last thing is that it could be the switch if a drink has been poured into it. I have all modules and switches in stock if you end up needing any
If you don't fancy doing it yourself we can do it at Falcon Performance in Teesside for you.
Good luck, Lee :thumbs: