As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DISCREPANCY: REFERENCE LP 186655 ITEM 1. AFTER SECOND ENGINE START DURING SINGLE ENGINE TAXI, WHEN APU BLEED DESELECTED IMMEDIATE SMELL NOTED IN COCKPIT AND CABIN VISIBLE SMOKE IN COCKPIT AND CABIN, IMMEDIATE RETURN TO GATE. CORRECTIVE ACTION: PERFORMED TS PER TSM 05-50-00-810-831-A. NO SMOKE OR SMELL DETECTED IN THE CABIN OR FLIGHT DECK. PERFORMED GVI OF ENG #2 NO DEFECTS FOUND.