I have a goodman gmp100-3 furnace. It fires up but then shuts off right away (within 5 sec). Led light blinks once. I replaced the flame sensor, and the flame looks good and strong. Why won't it keep lit and heat my home?

I have never seen a flame sencer go bad. What is the fault code for 1? Should be on the control, or on the back of the door. Most likely a pressure switch problem