As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING FLIGHT 3511, UPON GEAR RETRACTION THE LEFT MAIN GEAR WOULD NOT RETRACT. RECEIVED RED INDICATOR AND RED UNSAFE LIGHT IN GEAR HANDLE. CYCLED GEAR 3 TIMES WITH NO LUCK. AIR RETURN TO DTW. MAINTENANCE REMOVED ICE BUILDUP FROM BOTH LT & RT MLG WHEEL WELLS. CLEANED AND LUBRICATED BOTH MLG'S. PERFORMED 10 NORMAL GEAR RETRACTIONS AND EXTENSIONS. TESTS ALL CHECK GOOD AT THIS TIME.