As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED AN AIR RETURN FOR SMOKE IN THE CABIN & COCKPIT, BOTH AFT & FWD HAVE SMOKE. TOILET MASTER CAUTION MESSAGE. RAN QRH. INTEROGATED MDC, FOUND LAV FAN FAIL CODE B1-007306. RAN BOTH ENGINES IAW AMM 71-00-00, COULD NOT DUPLICATE SMOKE IN COCKPIT OR CABIN. OPEN