As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ATB/FUMES - RETURNED TO MSP DUE TO FUMES IN THE FLIGHT DECK AND CABIN. PERFORMED HIGH POWER ENGINE RUNS WITH NO ODORS FOUND. P-TRACK DATA INDICATED APU AS LIKELY SOURCE OF ODOR. APU INSPECTION IN WORK. FOUND #2 ENGINE AIR/OIL COOLER CRACKED. SAME REPLACED. (LP# 8056530)