As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FL300 PRESSURE DIFF INDICATING 4 PSID, ALT INDICATED 3500' DECREASED CABIN TO 1800' PRESS RELIEF LIGHT ON, NEITHER DIFF INDICATION OR ALT WERE GIVING CORRECT INFORMATION OPERATING IN STBY MODE. R & R CABIN ALT DIFF PRESS INDICATOR IAW MM 21-33-01, AND PERFORMED STATIC SYST. LEAK CHECK IAW MM 34-11-0 INDICATIONS NORMAL NO LEAKS NOTED. OPS CHECK NORMAL. CHECKED DRAIN TUBES FOR MOISTURE AND NONE FOUND.