As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ORD - FLT 4029 - ELECTRICAL/SMOKE SMELL ENTERED CABIN FOLLOWING THE STARTING OF ENGINES. MAINTENANCE WAS ABLE TO DUPLICATE SMELL PRIOR TO REMOVING. CLEANED AND REINSTALLED P2.5 SWITCHING VALVE ON RIGHT HAND ENGINE. PERFORMED OPS CHECK WITH NO INDICATION OF SMELL IN CABIN. AIRCRAFT WAS RETURNED TO SERVICE. (X)