As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING PREFLIGHT AFTER APU HAD BEEN RUNNING NORMALLY FOR APPROX 15 MINS (GEN ON BLEED OFF), THE APU QUIT AND THE APU FIRE CAS AND AURAL MESSAGE CAME ON. APU INITIATED AN AUTO SHUTDOWN AND THE SHARED APU BAGGAGE FIRE BOTTLE AUTO DISCHARGED WITH ACCOMPANING CAS MSG. EXTERNAL WALKAROUND NOTED NO INDICATION OF A FIRE. REMOVED AND REPLACED APU FIRE BOTTLE. OPS CHECK GOOD. IAW MM 26-20-30 & 26-10-10.