Door Lock Actuator

It is often part of the lock unit. It may include switches telling the car whether the door is open or locked. Failures are common on older cars. On many cars the lock unit is replaced as one part including the actuator, switches and latch.

Current in one direction locks, the other unlocks.

Buzzing, slow action or a door that does not lock show a worn actuator. A faulty door switch can keep interior lights on.