What was found
FLIGHT 2154. CABIN HIGH EICAS WARNING MESSAGE ABOVE 10,500. CREW MASKS WHERE DONED PASSENGER MASKS DID NOT DEPLOY. STOPPED CLIMB AND STARTED DESCENT. DECLARED EMERGENCY. LANDING UNEVENTFUL. LANDED BELOW MAX LANDING WEIGHT. MESSGE EXTNGUISHED BELOW 9800'. REMOVED FROM SERVICE. INTERROGATED CMC NO FAULT CODES FOUND RELATED TO CABIN HIGH EICAS MESSAGE. FOUND PRESSURIZATION MODE TO BE IN MANUAL MODE. PRESSURIZED A/C IAW E175 AMM 21-31-00-720-802-A. DEPRESSURIZED TO GROUND LEVEL. PRESSURIZATION MODE SWITCHED TO AUTO MODE. NDN. NO EICAS MESSAGES PRESENT. CREW O2 WITHIN LIMITS @ 1600PSI. COULD NOT DUPLICATE. NO PARTS REPLACED. RETURNED TO SERVICE.