As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING FLIGHT AT FLT LEVEL 360 THEY RECEIVED AN APU BLEED AIR LEAK WARNING. NOTE, APU WAS NOT OPERATING. TROUBLESHOOTING DISCOVERED THAT THE APU BLEED AIR LEAK DETECTION CONTROL UNIT PN 35009-20 WAS DEFECTIVE. A NEW UNIT WAS INSTALLED. OPERATIONS CHECKED OK.