As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU DET INOP ILLUMINATED AT CRUISE, APU WAS NOT RUNNING. GROUNDED - YES. FIRE DETECTION MODULE SHOWS APU-TAILPIPE. ACCOMPLISHED FIM 26-10 TASK 808. TAIL PIPE DETECTOR READS 25K OHMS. PER FIM 26-10 TASK 802 REMOVED AND REPLACED APU TAILPIPE OVERHEAT DETECTOR ELEMENT IAW AMM 26-15-01. INSTALLATION TEST GOOD. FIRE DETECTION CONTROL MODULE BITE CHECK GOOD. NO FAULTS.