As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
IAH TO MCI - DUE TO THE NR 2 IDG BEING ON MEL THE APU WAS REQUIRED TO BE RUN DURING THE FLIGHT. WHILE EN ROUTE TO MCI, THE CREW RECEIVED AN APU OIL TEMP CAUTION MESSAGE. THE CREW FOLLOWED THE QRH AND DIVERTED TO TUL. MAINTENANCE INSPECTED THE APU AND FOUND THAT IT WAS LOW ON OIL. AFTER SERVICING THE OIL, THE APU OPERATED NORMALLY AND WAS RELEASED FOR SERVICE.