What was found
GTF FLIGHT NR 2321: DURING LEVEL OFF AT 12000 'CABIN PRESS' MASTER WARNING ILLUMINATED. CABIN WOULD NOT PRESSURIZE IN THE AUTO MODE. CABIN PRESSURIZED BRIEFLY IN THE MANUAL MODE. C/W EMERGENCY/ABNORMAL CHECKLIST. MAINTENANCE INTERROGATED ECU. FOUND FAULT CODE 4101 ECU ANG CHANNEL 1. PERFORMED FIM TASK 21-60-00-810-843. FAULT CLEARED. NO DEFECTS NOTED. PERFORMED FUNCTIONAL TEST PRESSURIZATION CONTROL IAW AMM TASK 21-31-00-720-801. OPS CHECK GOOD. NO PARTS REPLACED. AIRCRAFT RETURNED TO SERVICE.