As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB OUT, COULD NOT CONTROL CABIN PRESSURE IN STANDBY OR MANUAL. AIRCRAFT RETURNED DTW, LANDED WITHOUT INCIDENT. PRESSURIZED AIRCRAFT TO 6 PSI IN MANUAL AC/DC, NO EXTERIOR LEAKS NOTED. PRESSURE HELD WITH APU AIR ONLY AND PACKS RUNNING, CONTROLLED RATE AND DESCENT THROUGHOUT ALL MODES OF MANUAL CONTROL PRESSURIZATION. SYSTEM CHECKED OK.