As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING ATTEMPTED APU START AFTER LANDING. APU FAULT LIGHT ILLUMINATED. GROUNDED - YES. REMOVED AND REPLACED START POWER UNIT REF B737-900 AMM 49-41-71-00-801 & 49-41-71-400-801, APU REMAINED INOP. REMOVED AND REPLACED APU START-GENERATOR. PART VERIFIED REF B737-900 AMM 49-41-21-000-801 & 49-41-21-400-801. OPS TEST NORMAL, TESTS PASSED. A/C OK FOR SERVICE.