As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
RETURNED TO DTW DUE TO AFT LAV FIRE WARNING AND STRONG ORDER IN CABIN. INSPECTED OIL QTY IN BOTH AIR CYCLE MACHINES, FOUND TO BE OK. DEFERRED LT PACK FOR TROUBLESHOOTING PER MEL 21-1. INSPECTED ALL DUCTING IN LT AC BAY AND FOUND NO LEAKS. REMOVED AND REPLACED LT AIR CYCLE MACHINE AND LT PACK COALESCER BAG PER M/M.