What was found
AIRCRAFT WAS GROUNDED: AN EMERGENCY WAS DECLARED INBOUND INTO ORD DUE TO THE FLIGHT CREW REPORTING THAT AFTER TAKEOFF ENROUTE TO ORD FLT ATTENDANTS REPORTED THAT DURING TAXI OUT & TAKEOFF THEY SMELLED FUMES BUT THE ODOR DISSIPATED SHORTLY AFTER TAKEOFF. ALSO ADVISED THAT THEY WERE FEELING LIGHTHEADED & THAT THEY HAD A COUPLE OF PAX FEELING LIGHT HEADED. THE FLT CREW REPORTED THAT THEY DID NOT NOTICE ANY ODOR IN THE COCKPIT. ACFT LANDED SAFELY AT ORD & TAXIED TO GATE UNDER ITS OWN POWER. MX PERFORMED SMOKE, ODOR, FUME TROUBLESHOOTING TASK CARD 26L00021001, & REPORTED NO ODORS DETECTED WHILE RUNNING ENGS & APU. MX COULD NOT IDENTIFY A SPECIFIC PART THAT WOULD HAVE CAUSED REPORTED ODOR.