As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFT CARGO FIRE TEST IN "NORMAL" WILL NOT TEST AND SHOWS "DETECTOR FAULT" "DET SELECT B." APPEARS INOP SYSTEM TESTS NOORMAL IN "DET SELECT A" POSITION. GROUNDED - YES. REMOVED & REPLACED AFT CARGO SMOKE DETECTOR (M2245). OPS CHECK GOOD REF B737-900 AMM 26-16-01.