As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU WOULD NOT SHUT DOWN AFTER ENGINE START. GROUNDED - YES. VERIFIED TERMINALS ON THE APU SWITCH ARE SECURE. ACCOMPLISHED APU BITE REF FIM 49-60 TASK 801. NO CURRENT FAULTS OR FAULTS IN HISTORY FOR APU SHUTDOWN. REMOVED & REPLACED ECU REF B737-800 AMM 49-61-12-400-801. 2 EA C/B'S OPENED & CLOSED. INSTALLATION TEST OPS CK GOOD PER THE SAME.