As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB, CABIN OVERPRESSURIZED AND CREW WAS UNABLE TO CONTROL CABIN PRESSURE IN BOTH AUTO AND MANUAL MODE. DEACTIVATED BOTH PACKS TO DEPRESSURIZE. AIRCRAFT RETURNED TO DTW AND LANDED WITHOUT FURTHER INCIDENT. FOUND INSULATION BLANKET OBSTRUCTING THE TRAVEL OF THE OUTFLOW VALVE. REMOVED BLANKET AND OPERATIONAL CHECK GOOD.