It's the actual door lock. There switches in it that make hte car electronically lock and open the doors with hte ket in the lock, and the switch that tells tha car the door is open worn out. And it eihter has to be replaced as a whole (like a $150 part) or you can try to do the fix yourself with a radioshack switch and a dremmil and glue. Growler has done it and he knows it alot better than i do.
***EDIT***
Here's a link to them on ECS. And i forgot to say that you vbasically have to get the the most innards of hte door to get to it.