As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) CABIN ALTITUDE WARNING HORN WAS ON DURING FLIGHT AND THE CABIN CLIMBED TO 10,000 FEET WITH 5.0 PSID. THE DUCT PRESSURE WAS 24 AND 26 PSID. AIRCRAFT RETURNED. SENSE LINE LOOSE AT LEFT PACK CONTROL VALVE. TIGHTENED LINE. AIRCRAFT SERVICEABLE.