As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LAVATORY SMOKE DETECTOR SOUNDED DURING TAXI OUT. SELECTED ENGINE BLEEDS OFF DURING RETURN TO GATE AND LAVATORY ALARM STOPPED. GROUND RAN BOTH ENGINES AND APU. OPERATED BLEEDS ON FOR 15 MINUTES. NO SMOKE OR ODORS DETECTED. NO SMOKE ALARM SOUNDED.