As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ETOPS SIGNIFICANT SYS - BTB -CABIN ALTITUDE INOPERATIVE AUTO EICAS MESSAGE. CABIN DESCENDED AT 2000 FPM. TURNED BOTH PACKS OFF WHEN DIFFERENTIAL REACHED 2 PSI. T/S IAW FIM 21-31-00, DID BITE TEST OF BOTH CABIN PRESSURE CONTOLLERS. NO FAULTS. CHECKED OUTFLOW VALVE CHECKED OK. RAN BOTH ENG AT THE GATE. CABIN PRESSURE OPS NORMAL. CABIN PRESSURE SYS OK FOR SERVICE.