As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED AN APU FIRE MESSAGE WHEN STARTING APU FOLLOWED BY AN APU FIRE FAIL MESSAGE. AFTER CHECKS WERE MADE USING THE AIRCRAFT MAINTENANCE MANUALS, MAINTENANCE REMOVED AND REPLACED THE FIRE DETECTION CONTROL UNIT. OPERATIONAL CHECKS USING THE AIRCRAFT MAINTENANCE MANUALS AND AIRCRAFT WAS RELEASED FOR SERVICE.