As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PHL FLT 1280 EN ROUTE CLT TO MHT, WHILE IN CRUISE FLIGHT, A "LAND ASAP" MESSAGE APPEARED ON THE ENGINE/WARNING DISPLAY UNIT, WITH NO OTHER INDICATIONS. THE ECAM RECALL FUNCTION DISPLAYED AN "APU FIRE" MESSAGE. THE FLIGHT DIVERTED TO PHL AND LANDED WITHOUT FURTHER INCIDENT. MAINTENANCE REPLACED THE APU FIRE DETECTION UNIT. SYSTEM CHECKS OK.