As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CLIMBING THROUGH 16000 FEET MASTER CAUTION LIGHT STARTED FLASHING AND THE CABIN DOOR ANNUNCIATOR ILLUMINATED. CREW RAN THE CHECKLIST, DECLARED AN EMERGENCY AND RETURNED TO DEPARTURE AIRPORT. LANDING WAS UNEVENTFUL. MAINTENANCE REPLACED THE MAIN ENTRY DOOR MONITOR PCB. A SUCCESSFUL OPERATIONAL CHECK FLIGHT WAS PERFORMED. AIRCRAFT WAS RETURNED TO SERVICE.