You can get cheap diagnostic tools at places like Checker or Advanced for around 80 bucks. There are ones like the Snap-on brick and the genesis that are around 3000 a piece. There is a program, which name illudes me at the moment but you can buy it online and they send you adapters so you can hook your laptop up to your car and pull codes that way, another nice feature of it is that you can just download updates whereas with the brick or genesis you have to get new cartridges. I'll post the name of the program if I can remember it