As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PHL/DTW - DURING TAKEOFF ROLL AT 50 KNOTS, RECEIVED AN AFT CARGO DOOR WARNING INDICATION. ABORTED TAKEOFF WITHOUT FURTHER INDICATION. INSPECTED THE AFT CARGO DOOR LINKAGE. CHECKED OK. CLEANED THE DOOR WARNING PROXIMITY SWITCH. OPERATIONAL CHECK OK.