As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED, RECEIVED A PASSENGER DOOR WARNING INDICATION. CREW ELECTED TO RETURN TO DCA AND LANDED WITHOUT INCIDENT. MAINTENANCE INSPECTED, TROUBLESHOT, REMOVED AND REPLACED THE CARGO DOOR HARNESS USING AIRCRAFT MAINTENANCE MANUALS. AIRCRAFT WAS RELEASED FOR SERVICE.