As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED APU OIL PRESSURE CAUTION MESSAGE IN CRUISE FLIGHT AFTER DEPARTURE FROM PHL. CREW FOLLOWED QRH, RETURNED TO PHL AND LANDED WITHOUT INCIDENT. MAINTENANCE INSPECTED, REMOVED AND REPLACED APU LOP (LOW OIL PRESSURE) SWITCH AND PERFORMED CHECKS USING AIRCRAFT MAINTENANCE MANUALS. AIRCRAFT RELEASED FOR SERVICE.