NV200 not locking

Hey

I have a NV200 which is converted to a fridge van. The van itself is only 2 years old but as its used in a business it has 118,000 miles.
Lately the central locking isn't working i'm thinking its something to do with a sensor on the door because the interior light wont turn off when the doors closed.
Its a pain because you cant see how much fuel is in the van because is always showing door open but the door isn't actually open.
Anyone got any suggestions?

Thanks