B767-300 and 300 ER
Fatigue; Situational Awareness; Troubleshooting
Aircraft Equipment Problem Less Severe
Flight Crew Diverted; Flight Crew Landed As Precaution; General Declared Emergency; General Maintenance Action
Aircraft
About halfway to MIA from [South America]; cruising at FL360; EICAS message Cabin Auto Inoperative displayed and caution beeper sounded.  Status messages also appeared for automatic cabin controllers 1 and 2.  Cabin altitude remained stable.  Confirmed on overhead pressurization panel that auto fail light was illuminated with auto selected.We called for the captain to return from his break immediately and ran the cabin automatic [pressurization] inoperative checklist.  This left us in manual mode for pressurization which was fine as the cabin was fairly stable around 6000 MSL as it had been at time of malfunction.  The captain returned promptly and we discussed options.  We had several hours left to go and had a good option in [ZZZ1] which had good weather.  With no backup other than manual for pressurization and now below max landing weight; we decided the best course of action was to divert there.  Captain informed dispatch and ATC.  The captain became Pilot Flying so the FB and I could focus on the divert and monitoring the pressurization.  We landed uneventfully and called maintenance.  Maintenance found a large water leak that had spread throughout the aft galley and into other areas of the aircraft where ice had formed.  With flight attendant duty time issues and concerns that the ice should be allowed to melt and drain for maintenance reasons; we stayed the night and continued home uneventfully with the same crew and aircraft the next evening.
A B767-300ER flight crew opted to divert to an enroute airport when both automatic pressurization controllers failed.