As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT CREW RECEIVED AN LAV SMOKE WARNING AFTER THE BLEED AIR SYSTEM WAS TRANSFERRED TO THE APU. THE AIRCRAFT RETURNED TO THE GATE. MAINTENANCE DETERMINED THAT THE APU WAS LEAKING OIL. THE APU WAS REPLACED AND THE AIRCRAFT WAS RELEASED FOR SERVICE.