What was found
CRUISE ALTITUDE 37,000 FT, AUTO FAIL LIGHT CAME ON. WHILE RUNNING THE CHECKLIST FOR AUTO FAIL, CABIN PRESSURE WAS UNCONTROLLABLE. CABIN COULD NOT BE CONTROLLED, DIVERTED, CABIN OXYGEN MASKS WERE DEPLOYED, AN EMERGENCY WAS DECLARED AND LANDED WITHOUT INCIDENT. THE AIRCRAFT WAS GROUNDED. FOUND ONE OF THE CABIN SAFETY PRESSURE VALVES TO BE UNRELIABLE, TEST FAILED. REPLACED BOTH UPPER AND LOWER PRESSURE RELIEF VALVES IAW AMM 21-32-01.