iif the cel isnt flashing when you have the code read its probably not going to pull any codes. i know with my truck when it was doing that. i put two different code readers on it at two different times and it wouldnt pull any codes, because it wont store the flashing codes. when a solid cel comes on is the only time you'll be able to pull it. my truck flashed on and off at random times for a couple weeks and i just drove it till the code finally came on for good. thats when i pulled it and threw new wires on it. people are probably going to disagree with me, but i went through the same thing. i never could read a code until it stayed on permanently.
07 Sport, 4.0, 4x4, leveled, 265 Duratracs, exhaust, intake, tune, stereo
08 6.4 F-350, smoked mirror and cab lights, H&S, 5" Flo-Pro, No Limit/XDP EGR delete