As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: PILOT RETURNED TO PHL ON ACCOUNT OF PACK FAULT ISSUE. NO EMERGENCY DECLARED. FLIGHT WAS NOT OVER WEIGHT AND LANDED WITHOUT ISSUE. MAINTENANCE REMOVED AND REPLACED THE LT ENGINE PRESSURE REGULATING VALVE CONTROLLER IAW AMM 36-11-19. OPS CHECK GOOD.