As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING T/C NG-21EA-23228-1 FOUND ZONE TRIM VALVE FAULT ON ZONE TEMP CONT 1. GROUNDED - YES. REF B737-900 FIM 21-62 TASK 835 FOUND AFT CABIN TRIM AIR MODULATING VALVE TO BE BAD. REMOVED AND REPLACED AFT CABIN TRIM AIR MODULATING VALVE REF B737-900 AMM 21-61-21. NO LEAKS NOTED. PERFORMED BITE TEST, TEST PASSED.