As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LEFT BLEED DUCT MASTER WARNING. AFTER 30 SECS CHANGED TO LEFT BLEED DUCT CAUTION. BOTH PACKS OFF AND PRESSURIZATION WOULD NOT HOLD. CAUTION MESSAGE WENT AWAY AFTER VALVES WERE CLOSED. DECLARED AN EMERGENCY AND DIVERTED. REPLACED LT PYLON LOOPS MT 202/203 AND AND REPLACED E-SEALS ON STUB DUCT ASSY IN PYLON. OPS CHECK AND LEAK CHECK GOOD.