As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAXI OUT WITH APU TURNED OFF. THE "APU DET INOP" & "OVHT/DET" MASTER CAUTION LIGHTS ILLUMINATED. PERFORMED APU FIRE DETECTION CONTROL MODULE BITE PER FIM 26 10 TASK 801 FAULTED APU TAIL PIPE FIRE DETECTION LOOP. REPLACED APU TAIL PIPE FIRE DETECTION LOOP PER AMM 26 15 01 400 801. PERFORMED APU FIRE DETECTION OPERATIONAL TEST PER AMM 26 15 00 710 801. OPERATIONAL TEST PASSED.