As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMBOUT, THE CABIN PRESSURE WARNING LIGHT ILLUMINATED. CABIN PRESSURE CLIMBED THROUGH 10,000 FEET TO 12,500 FEET WHEN CREW ACCOMPLISHED AN EMERGENCY DESCENT TO 10,000 FEET AND DIVERTED TO MKE. NO MENTION OF COM OR OF MANUAL PRESSURE CONTROL. LANDING WAS UNEVENTFUL. MAINTENANCE FOUND THE UPPER OF DOOR PRESSURE SEAL OUT OF THE RETAINER ON THE FORWARD INTEGRAL STAIRS. THE SEAL WAS REINSTALLED AND THE AIRCRAFT RETURNED TO SERVICE.