What was found
AIRCRAFT WAS GROUNDED: DURING CLIMB OUT NUMBER ONE ENGINE OVERHEAT LIGHT ILLUMINATED. AIRCRAFT HAS MULTIPLE MEL'S CONCERNING THE OVERHEAT/FIRE DETECTION SYSTEM. RAN SYSTEM TEST AND NO FAULTS WERE DETECTED. DURING CHECKLIST EXECUTION, AFTER RETARDING THE THRUST LEVER, THE OVERHEAT LIGHT EXTINGUISHED. DECESION MADE TO RETURN TO PHX AS A PRECAUTION AN EMERGENCY WAS DECLARED AND AIRCRAFT LANDED OVERWEIGHT WITHOUT INCIDENT. MAINTENANCE REPLACED ENG APU FIRE MODULE PER AMM TASK 26-10-01-400-8-01.