What was found
THE APU FIRE WARNING LIGHT AND BELL ACTIVATED, WITH APU OFF, WHILE EN ROUTE. THE APU FIRE BOTTLE WAS DISCHARGED, BUT THE LIGHT AND BELL CONTINUED TO ACTIVATE INTERMITTENTLY. THE AIRCRAFT WAS DIVERTED TO TUL WHERE IT LANDED WITHOUT INCIDENT. MAINTENANCE FOUND NO EVIDENCE OF FIRE. THE ENGINE/APU FIRE DETECTION MODULE WAS REMOVED AND REPLACED. THE APU WAS RUN WITH NO FIRE WARNING AND OPERATION CHECKING GOOD. IN ADDITION, THE APU FIRE BOTTLE WAS REMOVED AND REPLACED.