What was found
DURING CLIMBOUT (APU OFF) APU OVHT/DETR LIGHT ILLUMINATED MOMENTARILY THEN INTERMITTENTLY THE REST OF THE FLIGHT. GROUNDED-YES. C/W ENGINE/APU FIRE DETECTION CONTROL MODULE BITE PROCEDURE, REF B737-900 FIM 26-10 TASK 801. FOUND UPPER LOOP FAIL LIGHT CODE ILLUMINATED. FAULT CONFIRMATION, REF FIM 26-10 TASK 808. CHECKED RESISTANCE OF ALL LOOPS, FOUND TAIL PIPE AND LOWER LOOPS WITHIN LIMITS, CONFIRMED UPPER LOOP IS OPEN. REPLACED THE UPPER OVERHEAT DETECTOR ASSEMBLY, REF B737-900 AMM 26-15-01-000-801/400-801. ALL TEST PASS.