As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB PASSING FL 355 THE "CABIN ALTITUDE" LIGHT CAME ON WITH DIFFERENTIAL PRESSURE INDICATOR SHOWING ZERO. CABIN DID NOT LOSE PRESSURIZATION; HOWEVER THE CREW FOLLOWED THE CHECKLIST DECLARED EMERGENCY, DESCENDED TO LOWER ALTITUDE AND RETURNED TO THE DEPARTURE AIRPORT. UPON GROUND TEST NO ISSUES WERE FOUND WITH THE PRESSURIZATION INDICATION SYSTEM.