The most common failure on central locking on e30s (before i start, all Is have central locking from factory) is the locking ECU itself, which on euro cars is located in the drivers side (passengers side for american guys) footwell, behind the speaker cover, and is held in place by 2 x 8mm bolts. replacing this often fixes a lot of problems.
Another common fault is that from the factory, one of the wires leading to the motors themselves was a constant live, even with the ignition off. This meant over time, corrosion to the motor/wire itself was an issue. often a good fix is to pull up the drivers (again, to the american guys, passengers footwell and locate three wires, one of which is red. with the central locking ecu and loom removed, follow the red wire to this location and dont loose it. then, locate the socket for the interior light delay relay, and locate the solid red wire that goes into the relay socket. Cut this wire, and also cut the red wire located earlier, and join the two. This will solve about 80% of locking problems.
If the door pins cannot be operated, and none of the motors can be operated even by using the key, then the locking motors themselves have burnt out. Although there is a mechanical fuse in the central locking ECU itself to stop this form happening, the fuse itself runs on a heat basis. basicaly, if water contamintaes your central locking ECU and cools this fuse, your motors will burn out and will need to be replaced.
Firstly check fuse 27 though!
HTH
