As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CUSTOMER BOARDING, THE CABIN CREW NOTICED SMOKE IN THE CABIN. THE AIRCRAFT WAS DEPLANED NORMALLY THROUGH THE MAIN CABIN DOOR AND JET BRIDGE. CORRECTIVE ACTION: MAINTENANCE FOUND THAT THE APU WAS LEAKING OIL AND REPLACED THE APU. A DUCT BURNOUT WAS ACCOMPLISHED. THE AIRCRAFT HAS RETURNED TO SERVICE.