As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CLIMBING THROUGH FL 210, LOAD AIR RUSHING,WE LOOKED AT PRESSURIZATION AND IT WAS AT THE MAX DIFFERENTIAL AND WE STARTED DESCENDING WE SAW FAULT LIGHT ILLUMINATE FOR A FEW SECONDS,AS WE GOT TO FL190 PRESSURZATION OPERATED NORMALLY AND NO PROBLEMS FROM THERE. REMOVED FROM SERVICE. REPLACED AFT OUTFLOW VALVE IN REF TO Q-400 AMM TASK 21-31-16-000/400-801.PERFORMED FUNCTIONAL TEST IN REF TO Q-400 21-31-00-720-801.FUNCTIONAL TEST GOOD.A/C RETURN TO SERVICE.