As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CREW PREFLIGHT CHECKS (AIRCRAFT DOORS OPEN), APU FIRE AND APU AUTOSHUTDOWN DISPLAYED. - FOUND #1 APU GENERATOR MECHANICAL FAILURE CAUSING FIRE IN APU COMPARTMENT. FIRE CONTAINED TO APU COMPARTMENT AND WAS EXTINGUISHED BY CREW PERFORMING APU FIRE EXTINGUISHING PROCEDURE. ALL FIRE AND SMOKE DAMAGE REPAIRED AND APU WAS REPLACED, INCLUDING #1 GENERATOR.