As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE RECIEVE A "L PACK TEMP" EICAS MESSAGE. ACCOMPLISHED QRH CHECKLIST AND TURNED LEFT PACK OFF. EMERGENCY DECLARED. RETURNED TO FIELD. AIRCRAFT WAS GROUNDED. MAINTENANCE REMOVED AND REPLACED COMPRESSOR OUTLET SENSOR IAW AMM 21-51-06, TEMPURATURE CONTROL VALVE IAW 21-51-12 AND RAM AIR INLET ACTUATOR IAW AMM 21-53-03. OPERATIONAL AND LEAK CHECKS NORMAL.