Central Locking

All I can say on this matter is what happened to a friends 214Si which had the same trouble. A member of his familiy, on exiting the passenger side door, held the handle up, pushed the button down as if to lock it (fatal) and only managed to half close the door resulting in a screw up in the door mech. No amount of key twisting would release the door nor would the central locking release the internal mech. This went on for months.

In the end he had to get a matching internal replacement door panel trim from a breakers yard and then from the inside physically cut his way in through the existing internal door panal in order to release the mech which had apparently gone over center in its movement and was locked up solid. After releasing the door and making sure the operation was ok the new panel was fitted. Since then, no problems, and that member of the family knows better now.

PDH

I'd guess the central locking motors are either dead or dying, and/or the mechanism has got gunked up. WD40 won't harm anything - give it a go. It probably won't work though, so you'll have to remove the inside door trim (there's a step-by-step in the Haynes), and clean the system. If you need to replace anything, it won't cost too much from a scrappy - I think all the

We can't unlock the passenger side doors on our 620ti's tho either, there's not a hope of being able to turn the keys :)

The 600 doesn't have deadlocks tho, and if he can unlock it from the inside then there's definetely nothing wrong with the mechanism.

My guess is it's been changed at some point by a previous owner (e.g. after being broken into) and it's a different key...

the lock units themselves were very common to sieze up through lack of lubrication during manufacture, if you can open the door remove the door card, remove the lock assy, and free up using some good grease, i wouldnt reccoment WD-40 as this wont last, it may free things off, but it requires some good grease to keep it working correctly.

Many thanks to all who have offered advice - looks like it's out with the tools then ...

Thanks again chaps, and Happy New Year!

Cheers Dave