Phil, inexpensive scanners will do no more damage than resetting fuel/air trims to default which could make a deteriorating engine initially idle rough or be difficult to start. I do know of one instance where a poorly running engine would not start after a battery replacement which is the equivalent of clearing the DTCs that scanners can do. A "scanning/programming tool" is another animal. There are scanner / programmer tools but they tend to be expensive. Of the half dozen pcm tools that I own two of them will do programming and they are for my camaros. Again, the ones that can reprogram are what I consider expensive ie the DRBIII for our crossfires.