As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHEN L PACK SELECTED OFF NO PACK OFF LIGHT AND NO L PACK OFF MSG. TRIED PACK RESET AND BLEED RESETS BEFORE RETURNING TO GATE AT SHUTDOWN GOT PAC OFF MSG AND OFF LIGHT. CHECKED FLOW CONT VALVE L PACK CONNECTIONS. RESEATED L PACK CONTROLLER AND L PAC FLOW CONTROL CARD M863, ALL CKS NML.