As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB, COULD NOT CONTROL CABIN PRESSURIZATION. DESCENDED TO FLIGHT LEVEL 8,000 FEET AND CONTINUED TO GRR. AIRCRAFT LANDED WITHOUT INCIDENT. DTW MAINTENANCE REPLACED BOTH OUTFLOW VALVES AND PERFORMED PRESSURIZATION CHECK, CHECKED OK.