As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PRIOR TO PUSH BACK, APU SHUT DOWN, LATER THE APU FIRE WARNING AND BELL ILLUMINATED. PERFORMED APU FIRE CHECK LIST PROCEDURES PULLED AND ROTATED HANDLE. PERFORMED AN APU FIRE INSPECTION AND FOUND NO EVIDENCE OF FIRE. PLACED THE APU, APU FIRE DETECTION AND THE APU SQUIB LIGHT ON MEL, DEACTIVATING THESE SYSTEMS. OPERATED APU FIRE TEST IN OVERHEAT AND FIRE MODS NUMEROUS TIMES. APU AND FIRE DETECTION SYSTEM OPERATES NORMAL.