Rear power door lock not locking or unlocking work by hand but not power

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When I lock or unlock car doors with key fob or the power door lock button 3 of the 4 doors lock. Leaving one door that dose not seem to be conected to the rest of the power door lock. Power window still works on the door lights still come on when door opens and alarm will sound of door opens and alarm is set. Door will lock and in lock by hand.