As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING FIRST ATTEMPT TO START APU FAULT LIGHT ILLUMINATED. QRH PROCEDURE, WAITED 5 MINUTES, FAULT LIGHT WENT OUT. ON SECOND ATTEMPT LIGHT RE-ILLUMINATED AND APU DID NOT START. ACFT GROUNDED. R & R IGNITION PLUG IAW AMM 49-41-51. R & R IGNITION LEAD IAW AMM 49-41-52. R & R IGNITION UNIT IAW AMM 49-41-31. STARTED APU ON 1ST ATTEMPT. OPS CHECK GOOD.