As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU FAULT ILLUMINATED DURING CSS ATTEMPT AT FL380. QRH RAN, LIGHT EXTINGUISHED IMMEDIATELY WHEN APU START SWITCH TO OFF. SUBSEQUENT START ATTEMPT AT FL 360 SUCCESSFUL. ACFT GROUNDED. APU SUPPLY LINE AT THE FIREWALL INSIDE THE APU COMPARTMENT NOT SUFFICIENTLY TIGHT. TIGHTENED THE FUEL SUPPLY LINE IAW AMM 49-11-00-400-803 STEP 7L(6)(I).