As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: FLIGHT RETURNED TO BNA ON ACCOUNT OF PRESSURIZATION PROBLEM. AN EMERGENCY WAS DECLARED. MAINTENANCE ACCOMPLISHED BIT TEST OF BOTH PRESS CONTROLLERS, NO FAULTS IAW FIM 21-31, TASK 801. ACCOMPLISHED PRESS SYS GROUND TEST IAW AMM 21-31-00-700-802. BOTH CONTROLLERS PASSED. VERIFIED ALL CABIN DOOR GATES OPERATE. PUMPED AC TO 3 PSI TURNED OFF PACKS AND SLOW CABIN DECAY. PRESSURIZATION SYSTEM OK FOR SERVICE.