What was found
CABIN AUTO INOPERATIVE EICAS MESSAGE. CABIN ALT AUTO 1 AND 2 STATUS MESSAGE. AT FL 400, CABIN ALTITUDE WARNING, LOST CABIN PRESSURE. CREW COMPLIED WITH QRH, DROPPED TO 10,000 FL AND ELECTED MANUAL CABIN ALT CONTROL. DIVERSION TO KILN, ATC EMERGENCY DECLARATION. LANDING UNEVENTFUL WITH NO ADDITIONAL PRECAUTIONS. AIRCRAFT GROUNDED FOR UNSCHEDULED MAINTENANCE. REMOVED AND REPLACED POSITIVE PRESSURE RELIFE VALVE IAW BOEING 767 AMM 21-32-01. PERFORMED STATIC SYSTEM LEAK IAW BOEING 767 AMM 21-32-01-702-027. NO LEAKS NOTED. PERFORMED CABIN PRESSURE LEAK, AIRCRAFT PRESSURIZED TO 4.25 PSI. NO LEAKS, NO DEFECTS NOTED IAW BOEING 767 AMM 05-51-24. AIRCRAFT RELEASED TO SERVICE.