As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT FL 260, CABIN ALT INDICATED 8400 FT UNABLE TO CONTROL CABIN ALT IN AUTO/MANUAL MODE. COMPLIED WITH AOM VOL 1 EMER/ABNORMAIL PROCEEDURES. PERFORMED PRESSURIZATION CONTROL SYS OPS AND FUNCTIONAL TEST IAW AMM 21-31-00. OPS CHECKED GOOD. FUNCTIONAL CHECKED GOOD. COULD NOT DUPLICATE AT THIS TIME. THE ACFT WAS RETURNED TO SERVICE.