As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: AT FL410, RUMBLING NOISE THROUGHOUT ENTIRE AIRCRAFT. LEFT PACK AUTO SHUTDOWN, BURNING SMELL THROUGHOUT AIRCRAFT. CABIN AIR COMPRESSOR L2 AND L1 STATUS MESSAGE LT PACK EICAS MESSAGE. DECLARED EMERGENCY AND RETURNED TO DFW. FOUND CAC ADD HEAT VALVE BAD. REPLACED PER AMM 21-51-07.