As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON PREFLIGHT WE FOUND APU SWITCH ON BUT APU NOT RUNNING. AFTER FIRST APU START, APU AUTO-SHUTDOWN AND FAULT LIGHT ILLUMINATED. RAN QRH, WAITED FIVE MINUTES FAULT LIGHT EXTINGUISHED. STARTED APU SECOND TIME AND SAME RESULTS, AUTO SHUT-DOWN AND FAULT LIGHT ILLUMINATED. GROUNDED - YES. REMOVED & REPLACED APU, REF AMM 49-11-00-000-803 & AMM 49-11-00-400-803. OPS CHECK GOOD. LEAK CHECK GOOD. NO FURTHER DEFECTS NOTED.