As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
BTB DUE TO SMOKE IN COCKPIT DURING PUSHBACK. SUSPECT LEFT PACK OPEN DUE TO DMI ON LEFT PACK. LEFT PACK SWITCH WAS IN THE OFF POSITION. FOUND LEFT PACK FLOW CONTROL VLV OPEN CLOSE VLV PER MEL ITEM 7 STEP 1 OPS CK LEFT AND RIGHT PACKS ON GROUND LEFT PACK IS CLOSED AND WIRED RT PACK IS OPERATIONAL.