Does the passenger door lock operate the lock on the passenger door?
There's a wire connecting the driver door to the other 3 and
it goes under the carpet near the center under the back of the
driver seat. The 4 wires from the 4 doors are connected with a
metal connector and that can corrode, especially if there's been
water inside the car.
It's a wire that carries the communication signal between the
driver door module and the other doors.
Pictures from the internet:
There are 18 pictures in this imgur collection about repairing the connector.