As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU FAULT LIGHT ON ATTEMPTED START. STAYED ILLUMINATED, NO RESTART ATTEMPTED. ACFT GROUNDED. REMOVED AND REPLACED APU SHUTOFF VALVE IAW AMM 28-25-02, APU OPS CHECKED GOOD AND APU CURRENT STATUS SHOWS NO FAULTS. VERIFIED INSTALLED APU SHUTOFF VALVE.