What was found
APU RAN FOR 5 MINUTES, THEN SHUT DOWN WITHOUT A FAULT, RESTARTED, RAN FOR 5 MINUTES THEN SHUT DOWN WITH A FAULT LIGHT. PREFORMED APU BITE CHECK IAW AMM 49-61-05. FOUND ECU FAULTED. REMOVED AND REPLACED THE APU ECU IAW AMM 49-61-05. BITE TESTED OK. OPS OK. OK FOR SERVICE.