When locking the doors using any method (remotes, either armrest, key on driver's side), all doors do indeed lock, but the front passenger door lock immediately pops back up again - down-up, down-up each time I press "Lock". If I press Lock over and over again, it sometimes will eventually stay locked, but most often, I have to depress the lock manually. Just in case it would help, I checked the related fuses and they seemed fine.

Do I need a new door lock? Can I order it on ebay and replace it by myself? How? thanks a millions

 

My S60 did the same thing and then one day it fixed itself. Don't know what was wrong and what changed.

 

I had one that wouldn't go down all the way and I removed the insert that goes around the locking **** and reinserted it. It seems the ring had somehow gotten a tiny bit crooked and was stopping the **** from going all the way down. Could be something similar. Hope it helps.