Mercedes-Benz W201 central locking faults
W201: central locking does not work from any door, what is the fault?
Check fuse 12 first. Remove it completely, since just twisting it is not always enough, and also check the fuse's contact end. Next listen to the vacuum pump under the rear seat in its foam casing: it buzzes when locking and unlocking.
W201: the central locking pump buzzes but the doors do not lock?
The buzzing usually points to a vacuum leak. Check the vacuum hoses and connections; a common leak point is the fuel filler flap hose, which you can see through the boot. The leak can be found by listening to the hoses and bellows with the help of a thin hose. The locking vacuum diaphragms are in the four doors, the tailgate and the fuel filler flap, and a broken diaphragm prevents operation.
W201: why does the central locking blow a fuse?
The cause is usually a seized central locking motor or a faulty vacuum pump. A broken vacuum hose may also have been involved in the fault. It is worth checking the pump and its connector; the connector may have a crack. Replace the damaged part with a new one.