As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON FLIGHT 3816 DURING THE CLIMBOUT THE CREW RECEIVED A MESSAGE INDICATION THAT THE CARGO DOOR WAS OPEN. THE CREW ELECTED TO RETURN TO FIELD, AND LANDED WITHOUT INCIDENT. THE AIRCRAFT WAS REMOVED FROM SERVICE. PERFORMED BAGGAGE DOOR WARNING TEST IAW AMM 52-76-00 AND COULD NOT DUPLICATE THE PROBLEM. NO PARTS REMOVED OR REPLACED. THE OPERATIONAL CHECK WAS GOOD. THE AIRCRAFT WAS RETURNED TO SERVICE.