As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER ENG START CONT CAB ZONE TEMP LIGHT ILLUMINATES AND WILL EXTINGUISH ON MASTER CAUTION RESET. GROUNDED - YES. PERFORMED PZTC BITE #1 & 2. #2 PZTC SHOWS FLIGHT DECK TRIM VALVE FAULT. REMOVED AND REPLACED LEFT PACK, FLIGHT DECK TRIM VALVE V143 IAW B737-800 AMM 21-61-21.