As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON TAXI OUT WITH ENGINES SHUTDOWN APU SHUTDOWN WITH FAULT RE-STARTED AND FAILED AGAIN WITHOUT USING PNEUMATICS RETURNED TO GATE. FOUND NO APU AND PNEU LATCHED MSGS. CHECKED APU INLET PLENUM AND FOUND NO INGESTED FOD. OPERATED APU SEVERAL TIMES WITH PACK OPS AND BLEED PRESSURE NORMAL. REPLACED APU ECU. ROBBED APU ECU FROM A/C 1820, S/N 51-B0032, MFG P/N 2119590-101.