As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE APU FIRE DETECTION LIGHT ILLUMINATED WHILE ENROUTE FROM PHL TO IAH. THE APU FIRE BOTTLE WAS DISCHARGED, BUT THE WARNING LIGHT REMAINED ILLUMINATED. THE AIRCRAFT WAS DIVERTED TO ATL WHERE IT LANDED WITHOUT INCIDENT. MAINTENANCE FOUND NO EVIDENCE OF FIRE. THE APU FIRE DETECTION ELEMENT M334 WAS FOUND AT FAULT. THE FIRE DETECTION ELEMENT WAS REMOVED AND REPLACED. THE FIRE DETECTION SYSTEM PASSED ALL FUNCTIONAL TESTS. THE APU FIRE BOTTLE WAS REMOVED AND REPLACED IAW MM 26-22-00.