As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING VECTORS FOR APPROACH DESCENDING THROUGHOUT ABOUT 4500' MSL NOTICED A RED LIGHT IN THE APU FIRE HANDLE. NO WARNING BELL OR TRITONE. EXECUTED THE PHASE ONCE. GOT A NR 2 A NR 2 AGT 2 LOW CONFIRMATION. FIRE LIGHT WENT OUT. EMERGENCY DECLARED, CRASH/FIRE INSPECTED THE TAIL/APU AREA AND CONFIRMED NO FIRE. VISUALLY INSPECTED APU FIRE DETECTOR SENSORS NO DISCREPANCIES FOUND. REPLACED APU FIRE DETECTOR CONTROL UNIT, ALSO REPLACED APU FIRE SHUT DOWN RELAY R2-5095.