As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE FLIGHT, AUTOMATIC PRESSURIZATION WOULD NOT MAINTAIN CABIN AT FLIGHT LEVEL. AIRCRAFT RETURNED TO DTW AND LANDED WITHOUT INCIDENT. REPLACED CABIN PRESSURIZATION CONTROLLER AND PERFORMED AUTOMATIC AND MANUAL PRESSURIZATION TEST, OPERATIONAL CHECK OK.