As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE PERFORMING THE FIRE SYSTEM TEST, WE RECEIVED A FAULT LIGHT. THE FAULT LIGHT IS ASSOCIATED WITH "B" SIDE LOOP. WITH OVHT DET SWITCH IN THE "A" SIDE THE FIRE SYSTEM TESTS NORMAL. (FAILS ON ENGINE #1 LOOP SIDE B). GROUNDED - YES. VERIFIED, MOVED SWITCH BACK TO NORMAL AND FAULT LIGHT ILLUMINATED WITH B-LOOP UPPER FAN FAULT ON FIRE DETECTOR MODULE. REMOVED AND REPLACED #1 ENGINE UPPER FAN DETECTOR REF B737-800 AMM 26-11-01OPS NORMAL.