As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
EICAS MSG "CABIN AUTO INOP" AND "CABIN ALT AUTO 1&2" DISPLAYED. UNABLE TO CONTROL OUTFLOW VALVE USING MANUAL MODE. AT FL 230 THE CABIN ALTITUD LIGHT COMES ON AND THE CREW MADE A RAPID DESCENT TO FL 100. FIGHT RETURNED TO NEW YORK. AC MOTOR NR 2 WAS REPLACED IAW AMM 21-31-05/401 AND NR 2 SYSTEM TEST WAS PERFORMED IAW AMM 21-31-00/501 WITH NORMAL RESULTS. AUTOMATIC SYSTEM #1 WAS DIFFERED UNDER MEL 21-31-1 CAT "C".