What was found
DURING CLIMB THROUGH 11000FT WE GOT CABIN PRESS WARNING. RAN CHECKLIST AND NORMAL DESCENT. ALSO GOT FAULT LIGHT ON PRESSURIZATION CONTROL PANEL. RAN CHECKLIST, WENT MANUAL AND BACK TO AUTO. FAULT LIGHT CLEARED BUT MAN DIFF WAS STILL AT ZERO. CABIN ALT RATE MAINTAIN SAME ALT AS AIRCRAFT. EMERGENCY WAS DECLARED. LANDING UNEVENTFUL. REMOVED FROM SERVICE. INSPECTED DOOR SEALS, NO DEFECTS FOUND, PRESSURIZED A/C NO LEAKS FOUND. INTERROGATED CDS + FOUND CBPC OUTFLOW VALVE FAIL MSG. REPLACED OUTFLOW VALVE PER AMM TASKS 21-31-16-00-801 + 21-31-16-400-801 OPS CHECK GOOD. UNABLE TO DUPLICATE PROBLEM, OUTFLOW VAVLE REPLACED AS A PRECAUTIONARY MEASURE. AIRCRAFT RETURNED TO SERVICE.