As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SHIP 5646 - SMKE - WHILE BOARDING AT GATE SMOKE STARTED FILLING UP THE FLIGHT DECK AND CABIN WHILE APU RUNNING. GROUND CREW NOTE APU SMOKING OUT THE EXHAUST. CORRECTIVE ACTION: CONFIRMED APU FAILURE WITH OIL TANK EMPTY AND METAL ON THE CHIP DETECTORS, APU REPLACED. PERFORMED DUCT DECONTAMINATION AND REPLACED RECIRC FILTERS. NO ADDITIONAL SMOKE OR ODORS PRESENT.