As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHEN NR 2 BLEED WAS SELECTED ON, GREY HAZE FILLED COCKPIT AND CABIN. MAINTENANCE REPLACED NR 2 ENGINE P2.5/3.0 SWITCHING VALVE IAW QX MTC 9723001. GROUND RAN NR 2 ENGINE, SELECTED NR 2 BLEED ON. NO HAZE OR ODORS DETECTED. AIRCRAFT RETURNED TO SERVICE.