As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PHX - FLT 742 - ELP TO LAS DURING CRUISE, APU FIRE LIGHT AND BELL CAME ON. APU PREVIOUSLY PLACARDED, FIRE EXTINGUISHING SYSTEM INOP. CREW PULLED FIRE HANDLE AND WARNINGS CEASED. CREW ELECTED TO RETURN TO PHX. MAINTENANCE FOUND LOOP-M 334 OUT OF TOLERANCE, REPLACED M 334 AND CLEANED PLUG D 4816. SYSTEM OPS CHECKED OK, AC RETURNED TO SERVICE. (W)