What was found
APU FAULT. DURING THE APU TROUBLESHOOTING, FOUND THE ECU UNABLE TO SHOW ANY KIND OF MESSAGE AND CODE. REMOVED AND REPLACED ECU IAW AMM 49-61-05-40. REMOVED AND REPLACED APU STARTER IAW AMM 49-41-01-004-001 & 49-41-01-404-007. APU STARTED & RAN NORMAL. REMOVED AND REPLACED THE PRESSURE SENSOR IAW AMM 49-61-04-002-001-402-006. APU OPS CHECKED GOOD. REMOVED AND REPLACED SURGE CONTROL VALVE IAW AMM 49-53-01-401. NO HELP. REMOVED AND REPLACED ECU IAW AMM 49-61-05. OPS CK NORMAL.