My Goodman furnace will light and then go out. This will occur 3 times, then will quit running. The control board blinks 1 time and tells me to Check Gas flow, gas pressure, gas valve, and flame sensor. It seems to have gas going to the valve. Could this be a bad gas valve? Or a bad Flame sensor?

My guess is that you have a problem with the flame sensor. This is something that looks like a heavy wire sticking up into the flames of the burner. The wire then goes to a ceramic base with a wire coming out of it. This will be secured to the furnace with a screw. Undo the screw, slip the ceramic and wire out of the hole provided for it and than use a piece of fine sandpaper on the wire part of the sensor that goes up into the flame. Shine this wire good with the sandpaper and then replace it back into the hole and secure it. Try the furnace again it should light and stay lit, if it goes out once and then right back on that may be normal but if it lights and goes out for several times and then does not light at all you may have to have a new flame sensor. They are easy to replace. Just go one step further than you did when you cleaned it and that is to unplug the wire from when the ceramic is and that is it.

My guess is that you have a problem with the flame sensor. This is something that looks like a heavy wire sticking up into the flames of the burner. The wire then goes to a ceramic base with a wire coming out of it. This will be secured to the furnace with a screw. Undo the screw, slip the ceramic and wire out of the hole provided for it and than use a piece of fine sandpaper on the wire part of the sensor that goes up into the flame. Shine this wire good with the sandpaper and then replace it back into the hole and secure it. Try the furnace again it should light and stay lit, if it goes out once and then right back on that may be normal but if it lights and goes out for several times and then does not light at all you may have to have a new flame sensor. They are easy to replace. Just go one step further than you did when you cleaned it and that is to unplug the wire from when the ceramic is and that is it.
That's probably it.