What was found
APU FAILED TO START AT FL 370 WITH FAULT LIGHT ILLUMINATING FOR OVER 5 MINUTES. ACFT GROUNDED. PERFORMED APU BITE IAW FIM 49-60, TASK 803. FAULT HISTORY LOGGED 1 MAINT MESSAGE 49-31016 OVERTEMP SHUTDOWN. COMPLETED FIM TASK 49-30, TASK 803. APU STARTS & RUNS NORMAL ON GROUND. NO CURRENT OR ACTIVE FAULTS. REPLACED THE STARTER GENERATOR IAW AMM TASK 49-41-21-400-801, OPS CHECKED GOOD. REPLACED APU FCU IAW AMM 49-31-11. OPS & LEAK CHECKED GOOD, IAW 49-11-00.