As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DFW - FLT 581 - EN ROUTE ORD-SAT, DETECTED APU FIRE WARNING LIGHT AT MFDU. DISCHARGED APU FIRE BOTTLE. DIVERTED DFW AND LANDED WITHOUT FURTHER INCIDENT. REPLACED APU TAIL PIPE OVERHEAT DETECTOR RELAY. SYSTEM GROUND CHECKED NORMAL OPERATION. (M)