As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF FROM IAD RECEIVED A LANDING GEAR DISAGREE CAUTION MESSAGE, CREW DECLARED AN EMERGENCY AND RETURNED TO THE FIELD. FLIGHT LANDED WITHOUT INCIDENT. ADJUSTED GAP TO THE LEFT MLG UPLOCK ASSEMBLY AND PERFORMED AN OPERATIONAL TEST OF THE PROX SENSOR SYSTEM AND FUNCTIONAL TEST OF THE EXTENSION AND RETRACTION SYSTEM. OPERATIONAL AND FUNCTIONAL TEST SATISFACTORY, NO DEFECTS NOTED.