As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON GROUND, APU SHOWED FIRE WARNING, VISUAL FIRE CONFIRMED, BOTTLE DISCHARGED. ON INVESTIGATION, THE INNER EXHAUST DUCT V BAND CLAMP BROKE SENDING HOT AIR INTO THE SPACE BETWEEN THE INNER AND OUTER EXHAUST PIPE IGNITING RESIDUAL OIL AND FUEL. APU WILL BE REPLACED.