As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF DURING CLIMB, COULD NOT CONTROL AIRCRAFT CABIN PRESSURIZATION IN AUTO OR MANUAL MODES. AIRCRAFT RETURNED TO DTW DUMPING 20,000 LBS OF FUEL BEFORE LANDING WITHOUT INCIDENT. REPLACED THE RIGHT PACK VALVE AND CLEANED BOTH OUTFLOW VALVE SHAFTS. AIRCRAFT PRESSURIZED TO 3 PSI, LEAK CHECKED IN BOTH AUTO AND MANUAL MODES, SYSTEM CHECKED OK.