As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
NO DUCT PRESSURE FROM APU. LOW AIR PRESSURE FROM APU. APU PRESSURE RETURNED TO NORMAL. REOPENED BY ORD MM FOR: LOW BLEED PRESSURE PROBLEM RETURNED. REPLACED APU AIR FLOW SENSOR MODULE. APU DUCT PRESSURE CONSTANT NOW AT 28 PSI. OPERATES BOTH PACKS AND DRY MOTORS ENGINES TO START.