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Based on your description, I suspect a problem with the central locking control module.
The first thing I would check would be to remove any floor mat you may have on the driver's side and feel the carpet. If it's wet, you have a water intrusion issue. You should also feel the carpet in the rear as that tends to be a lower area. Usually when water is in the driver's side, it gets in through the bonded windshield seal (glue) from a improperly replaced windshield. The central locking control unit is located under the carpet immediately in front of the driver's seat. The carpet must be lifted, the box housing the controller must be removed, and the controller inspected for water intrusion. I have had luck taking the controllers apart and drying them out. But if it has been awhile it may require replacement. Also check the passenger side. The controller for the automatic transmission (if so equipped) is housed at the passenger's feet.
If water intrusion is not the issue, I suggest you take the vehicle to a repair shop that has a scanner capable of interrogating the central locking control module and checking for any stored Diagnostic Trouble Codes (DTCs). Further testing, diagnosis and repair would be based on any DTC(s) retrieved.
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