I can't get any codes at all. I am trying to figure out why my truck is running terribly...Thought it was bad gas, nope, gas looks good. New filter, pump is fine. Thought it might be EGR valve. Pulled it, looks fine. Is it true that all sensors throw codes? And what if I am completely unable to check them? Do I have a main computer on the fritz? Please help, I don't want to call a tow truck to take it someplace that'd do the same thing I could do (except know what the problem is ) Thanks!