As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FDR SYSTEM PARAMETER REASONABILITY CHECK SHOWS A PROBLEM WITH THE APU ECU FAULT DISCRETE SHOWING FAULT. ACFT GROUNDED. REMOVED AND REPLACED APU ECU, INSTALLATION CHECKS GOOD IAW AMM 49-61-12, APU DIGITAL DATA BUSS SIGNAL TEST CHECKED GOOD IAW AMM 31-31-00. PERFORMED FIM 49-60 TASK 81, APU BITE PROCEDURE, NO FAULTS FOUND.