I have a 1999 GMC Savanna 2500 that was running fine. I actually sold it on EBAY and the day before they were to pick it up it would not start. It has no spark (coil and ign module are fine), fuel pump kicks on for only a second or two, then shuts off. A mobile mechanic came by, put his scanner on it and got nothing, as if his scanner was bad. Checked his scanner on his vehicle and it worked. Mechanic told me it was either the ECM (though investigated and I think it has none) or the PCM. Any thoughts on what the problem is? Does a junkyard PCM need to be programmed or can it just be put in?