What was found
2 APU START ATTEMPTS NO START WITH APU FAULT LIGHT. BITE CHECKED THE ECU. HAVE AUTOSHUTDOWN. NO COMPONENT FAULT. WILL NOT START. REPLACED APU. REPLACED APU BATTERY CHARGER PER SERVICE TIP DUE TO APU NO START AND PNEUMATIC FLUCTUATIONS. OP CHECKS GOOD FOR ONE START AND APU FAILED AND AUTO SHUTDOWN AFTER SECOND START, WITH APU FAULT AND GEN FILTER FAULT. FOUND GEN DIFF PRESS SWITCH BAD. READS OPEN WITH NO PRESS AND VARYING OHMS WHILE TAPPED, 16OHMS TO INFINITE. REPLACED PRESSURE SWITCH.