As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER DEPARTURE, SMELLED PRESENCE OF SMOKE. RECIEVED A MASTER WARNING FOR SMOKE IN THE AFT LAVATORY. RETURNED TO DEPARTURE. R & R THE AFT LAVATORY FAN AND PERFORMED AN OPS CHECK IAW AMM 21-23-93. AFTER REPLACEMENT, PERFORMED HIGH POWER RUNS FOR APPROXIMATELY 30 MINUTES WITH NO FURTHER DEFECTS NOTED. THE ODOR DISSIPATED, NO SMOKE NOTED, AND EICAS REMAINED CLEAR OF MESSAGES.