As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED LOST AUTO PRESSURIZATION. CABIN PRESSURE CLIMBED TO 8400FT, NO EICAS MESSAGE PRESENT. CREW PERFORMED AIR RETURN. MX R & R DIGITAL PRESSURE CONTROLLER AND ALSO R & R ELECTROPNEUMATIC OUTFLOW VALVE WITH OPS CHECKS SUCCESSFUL. ACFT WAS APPROVED FOR RETURN TO SERVICE.