As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FAULT LIGHT ILLUMINATED WHEN ATTEMPTING TO START APU. ACFT GROUNDED. INTERROGATED APU CDU, FOUND FAULT 49-41181, IAW FIM TASK 49-40 TASK 805. REMOVED AND REPLACED THE IGNITION UNIT IAW AMM 49-41-31. APU STARTED, NO CURRENT FAULTS IN CDU.