As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU BLEED PRESS SHOWS 0 TO MAX OF 4 PSI. SELECTED BLEED SWITCH TO OFF VALVE CLOSED NORMALLY. AFTER A REVIEW OF HISTORY AND TROUBLESHOOTING, FOLLOWED SERVICE TIP 49-11-00 PAGE 200A. ECU MSG. REVERSE FLOW. REPLACED APU BATTERY CHARGER PER AMM, CHK'D GOOD. APU STARTED AND RAN NORMAL, PNEUMATICS OPS. NORMAL, SHUT DOWN CHK'D. ECU NO MSG'S. REACTIVATED SYSTEM PER MEL 3611G.