As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SHORTLY AFTER DEPARTURE, WE GOT THE SMOKE TOILET CAUTION MESSAGE. COMPLETED EMERG NON-NORMAL CHECKLIST. INDICATION WAS REMOVED. NO SMOKE WAS EVER SEEN BY F/A OR PASSENGERS. RETURNED TO DEPARTURE. WE WERE NOT DE-ICED PRIOR TO T/O. REPLACED SMOKE DETECTOR (AFT LAV) IAW AMM 26-16-01. ACCOMPLISHED OPS TEST IAW AMM 26-16-01. OPS CHECK GOOD. PN ON/OFF: PU90-421R3, NSN. COMPLIED WITH EO NR C25025 (LAV AIR VENT COVER).