What was found
DURING CRUISE AT 37000 FT, AUTO FAIL LIGHT ILLUMINATED. RAN QRH & SWITCHED TO ALTERNATE. ALL PRESSURIZATION INDICATES NORMAL. ACFT GROUNDED. CONFIRMED FAULT. NR 1 CABIN PRESSURE CONTROLLER SHOWS P5 OVERHEAD CABIN PRESSURE CONTROL MODULE LRU FAULT. REPLACED CABIN PRESSURE CONTROL MODULE IAW AMM 21-31-02, AND AS PRECAUTION, REPLACED AFT OUTFLOW VALVE ASSY IAW AMM 21-31-03, PRESSURIZATION GROUND TEST NORMAL IAW AMM 21-31-00, FIM 21-31, TASK 801.