As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DIVERTED DUE TO RED "APU FIRE" CAS POSTED AFTER TAKEOFF. CREW DEPRESSED APU FIRE SWITCH AND EXT BUTTON. THERE WERE NO FURTHER INDICATIONS OF FIRE. AIRCRAFT LANDED WITHOUT INCIDENT. INSPECTION REVEALS NO EXTERIOR OR INTERIOR SIGNS OF FIRE OR DAMAGE. REPLACED FIRE DETECTION AND EXTINGUISHING SYSTEM CONTROL UNIT, APU SENSING, FIREWALL SENSING AND EDUCTOR SENSING ELEMENTS ALONG WITH THE NR 2 FIRE BOTTLE, GREEN AND RED SQUIB, AND APU SQUIB. OPS CHECK GOOD.