As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT 7958 - MLI - EN ROUTE TO ORD, FLIGHT CREW REPORTED AND APU FAIL MESSAGE FOLLOWED BY AN APU FIRE MESSAGE. MAINTENANCE PERFORMED AN INSPECTION OF THE APU TAIL PIPE AND APU COMPARTMENT. NO EVIDENCE OF FIRE COULD BE FOUND. DEFERRED THE APU FIRE DETECTION SYSTEM.