What was found
APU FAULT LIGHT ILLUMINATED. TWO RESTARTS WERE ATTEMPTED AFTER FIVE MINUTE INTERVALS IAW ATTEMPT. AFTER EACH ATTEMPT WITH APU SWITCH OFF, FAULT LIGHT EVENTUALLY EXTINGUISHES. R & R MAIN & AUXILIARY BATTERIES. ACCOMPLISHED OPC CHECK OF MAIN AUXILIARY BATTERIES. MAIN & AUX BATTERIES, OPS CHECKED GOOD IAW AMM 24-31-11-000-802-002 & 24-31-11-400-802-002. AFTER MAIN & AUX BATTERY CHANGE APU WILL NOT START, WITH FAULT LIGHT. APU FAULT 49-61223 CURRENT, AIR TEMP SENSOR SHORT CIRCUIT. PERFORMED FIM 49-60. FOUND INLET TEMP SENSOR INOPERATIVE. REMOVED /INSTALLED TEMP SENSOR REF 49-61-341-000-801/400-801. RETURNED ACFT TO NORMAL. PERFORMED APU OPS CK IAW 49-11-00-710-801. SYS CKS NORMAL.