2007 C5 MK2 P0483 FAULT

[wurlycorner]

That sounds very odd - the only way locking/unlocking could interfere with it, would be via the BSI (which controls door lock/unlock) but on the schematic for your car, there's no link (either directly or indirectly) on circuits between the BSI and the fan control unit.

It might be worth trying a BSI reset (no harm in doing) in case there's some strange behaviour from the BSI that is causing strange behaviour in the engine compartment fuse box (which is in the feed - albeit still no direct link to the BSI).
If not, then (extreme long shot) I would suggest checking all the connectors in the whole circuit that runs from battery to to see if there is any stray contamination of some sort, bridging across connectors and causing a false feed/false ground? As I say, that's a real long shot though... Otherwise it must be something like a sticking relay in the fan control unit or a fault in the Engine ECU?

[sydo]

That sounds very odd - the only way locking/unlocking could interfere with it, would be via the BSI (which controls door lock/unlock) but on the schematic for your car, there's no link (either directly or indirectly) on circuits between the BSI and the fan control unit.

It might be worth trying a BSI reset (no harm in doing) in case there's some strange behaviour from the BSI that is causing strange behaviour in the engine compartment fuse box (which is in the feed - albeit still no direct link to the BSI).
If not, then (extreme long shot) I would suggest checking all the connectors in the whole circuit that runs from battery to to see if there is any stray contamination of some sort, bridging across connectors and causing a false feed/false ground? As I say, that's a real long shot though... Otherwise it must be something like a sticking relay in the fan control unit or a fault in the Engine ECU?

I'll try resetting the BSI. It's a strange problem, really. So, what are the instructions for resetting the BSI?

[mickthemaverick]

You'll find the procedure here: viewtopic.php?p=601679#p601679

[myglaren]

BSI reset procedure