As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU FAULT LIGHT ILLUMINATED. APU SHUTDOWN. GROUNDED - YES. COMPLETED FIM 49-90 TASK 809 THROUGH STEP F(2)(I), FOUND FILTER BYPASS VALVE LOOSE, CAME OUT WITH FILTER ELEMENT. INSTALLED BYPASS VALVE REF CMM 49-90-57 PAGE 733 ITEM (16). RAN APU, LEAK CK GOOD. NO CURRENT FAULTS. BOTH FILTER ELEMENTS SHOWED NO CONTAMINATION.