As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE PARKED AT GATE WITH ENGINES SHUT DOWN, MASTER CAUTION ILLUMINATED WITH AUTO FAIL & ALT MODE ILLUMINATED. GROUNDED - YES. REMOVED AND REPLACED AFT OUTFLOW VALVE ASSY IAW AMM 21-31-03/401. PRESSURIZATION SYSTEM MANUAL AND GROUND TEST TESTED GOOD.