As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAKEOFF THE SECONDARY OUTFLOW VALVE WOULD NOT CLOSE. WE PERFORMED THE FUNCTIONAL CHECKS OF THE OUTFLOW VALVES AND FOUND THAT THE SECONDARY VALVE WOULD NOT CLOSE PROPERLY. WE REMOVED AND REPLACED AND THE SYSTEM BEGAN TO FUNCTION PROPERLY.