As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER GETTING APU GEN ONLINE THE OVERSPEED LIGHT ILLUMINATED AND APU GEN KICKED OFF LINE RE-ESTABLISHED GEN 1 AND 2 RAN QRH AND AFTER 5 MIN OVERSPEED LIGHT EXTINGUISHED. GROUNDED - YES. RAN APU BITE REF B737-900 FIM 49-61 TASK 801 NO CURRENT FAULTS FOUND. SPEED SENSOR FAULT FOUND TO BE INTERMITTENT. NO FAULTS LOGGED AFTER APU OPS CHECK. APU GROUND VERIFICATION CHECKS NORMAL.