As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: FLIGHT RETURNED TO SFO ON ACCOUNT OF NUMBER ONE BLEED LOW PRESSURE RESULTING IN A PACK PROBLEM. AN EMERGENCY WAS DECLARED. MAINTENANCE INSPECTED SENSE LINES AND PERFORMED OPERATIONAL CHECK ON NR 1 ENGINE BLEED AIR SYSTEM IAW AMM 36-11-00. OPS CHECK GOOD. PERFORMED BITE ON BMC #1. NO FAULTS NOTED.