As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CABIN PRESSURE DIFFERENTIAL GUAGE FLUCTUATES IN FLIGHT AT FL 350. N1 LEFT 87.1, RIGHT 87.0. WOULD VARY BETWEEN -100 TO + 200 - 400 FPM. ACFT GROUNDED. C/W B737-900 FIM 21-31 TASK 801 CABIN PRESSURE CONTROLLER BIT PROCEDURE, BOTH SYSTEMS 1 & 2 TESTED GOOD. NO CURRENT FAULTS NOTE , GROUND VERIFICATION GOOD.