As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED THAT DURING CLIMBOUT THEY RECEIVED A LAVATORY SMOKE WARNING MESSAGE. FLIGHT ATTENDANT VERIFIED THAT THERE WAS NO SMOKE OR ODOR IN THE CABIN. DECLARED AN EMERGENCY AND RETURNED TO FIELD. MESSAGE CLEARED ON LANDING. MAINTENANCE INSPECTED THE AIRCRAFT AND FOUND NO EVIDENCE OF FIRE OR SMOKE IN THE LAVATORY. LAVATORY SMOKE DETECTOR REPLACED. OPS CHECKED GOOD WITH NO FURTHER DEFECT NOTED.