As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PDX - FLIGHT 2591 - GOING THROUGH 8000 FEET, FLIGHT ATTENDANT CALLED TO SAY THAT THERE WAS AN EXHAUST ODOR IN THE BACK OF THE AIRCRAFT. STRONGEST AFTER TAKEOFF, BUT DISSIPATED BY THE TIME SHE CALLED. RETURNED TO THE FIELD AND ACCOMPLISHED A UNEVENTFUL LANDING. MAINTENANCE PERFORMED A INSPECTION OF THE APU AND ENGINE GROUND RUN, WITH NO DEFECTS NOTED. AIRCRAFT RETURNED TO SERVICE. NO PARTS REPLACED.