As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ORD - FLT 4173 - DURING TAXI, FLIGHT CREW REPORTED SMOKE COMING FROM PASSENGER READING LIGHT AT SEAT 7A. MAINTENANCE REMOVED AND REPLACED THE PASSENGER SERVICE UNIT PCB ASSEMBLY AT ROW 7 IAW EMB MM. OPERATIONAL CHECK WAS GOOD AND AIRCRAFT WAS RETURNED TO SERVICE. (M)