As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE PERFORMING TSR 908005, FAULT CODE 49-41011 DISPLAYED ON APU BITE CHECK AND FAULT LIGHT ILLUMINATED. ACFT GROUNDED. DURING APU START UP NO NOISE HEARD FROM THE IGNITER PLUG. REPLACED IGNITER PLUG AND APU IGNITION UNIT REF AMM 49-41-51 AND 49-41-31. OPS TEST GOOD, BITE CHECK GOOD.