As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAKEOFF CLIMB HAD GEAR WARNING INDICATION. AIRCRAFT RETURNED TO DTW AND LANDED WITHOUT INCIDENT. PERFORMED SYSTEM CHECK OF MAIN LEFT LANDING GEAR UPLOCK. REPLACED BOTH LEFT MAIN GEAR UPLOCK SENSORS. CHECKED AIR GAP AND PERFORMED GEAR SWING, OPERATIONAL CHECK OK.