As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER PUSHBACK IN ATL AFTER FIRST ENG START AND SELECTING SECOND PACK TO OFF THE APU SHUTDOWN W/APU FAULT MSG DISPLAYED. BITE CHECK OF APU ECU FAULTS REVERSE FLOW. FWD APU BLEED AIR TO MCO/PLAC PER MEL 49-11-01C. T/S PER FIM. REMOVED AND REPLACED APU SURGE BLEED CONTROL VALVE PER MM. CHKS OK MCO AND PLAC REMOVED.