As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FAULT LIGHT DURING APU START ATTEMPT. GROUNDED - YES. PERFORMED APU BITE PROCEDURE IAW B737-9 AMM 49-61-00, NO FAULTS FOUND AS PRECAUTIONARY REMOVED AND REPLACED APU ELETRONIC CONTROL UNIT IAW AMM 49-61-12 GROUND VERIFICATION SUCCESSFUL.