No to hijack the thread, but the mention of scanners brings to mind a story of a neighbor of mine, very car challenged, who had a jeep that wouldn't run right at all, the thing would rev, stumble, stall, straighten out a little, all the gages would jump all over the place. I returned from a vacation and the car was gone. I asked him and he said it was at the garage but it wasn't looking good. He told me that he was going to just donate it. I asked if I could have a crack at it. He said sure. I went to the repair garage and asked for the keys. The owner asked me what I was going to do with it, I told him I was going to fix it and sell it. He laughed out loud at me and said he has had his 2 best guys on it for a week, that the engine was a bone yard replacement from a different year and that it was a "transitional" model of engine computer so that none of the codes were necessarily right. I'll take my chances I told him. The battery was dead and if I jumped it, it would start, and croak as soon as the jumpers were removed. I brought down a charged battery got it to run but even with my foot halfway into it the rpms would vary wildly and it was surging like crazy. They also had bundles of wire hanging out from under the dash, the steering column and in the engine bay. I managed to drive it the 2 miles to my house and proceeded to re assemble all the wiring and such. I got it running again and started watching the battery voltage. It was jumping all over the place and then it would steadily head downhill until all the gages would **** out and then it would eventually do a few more weird revs and then die. The guys had all kinds of voltage information written down on pieces of paper in the truck when I got it. But the main battery voltage jumping all over the place made me curious. I took the alternator down to the local parts jockey and they tested it, the thing was putting out all different voltages at a steady speed. I installed a rebuilt, fired it up and it ran perfectly. I sold it to a guy who does hardwood floors for me occasionally. Over 2 years later I thought to ask him about the truck. "never missed a beat in all the time I've been driving it."
The moral of the story is that although automobiles have all kinds of sophisticated electronics in them these days, some of the same stupid non-computer related stuff that croaked them before computers will still croak them today. Look for the basics, vacuum leaks, bad grounds...alternators with split personalities!