Now for the bad. What is missing is the customization of the AVG (MPG) on the main display. People will use ScanGauge to improve driving habits and improve MPG. The AVG resets itself after every trip. The AVG should be user selectable, with a running AVG based on TRIP, DAY, WEEK, MONTH or ENDLESS so that long term MPG progress can be measured on the main screen. As this product is marketed as an item to improve economical driving habits, this is a glaring omission of a basic functionality that seriously limits an otherwise outstanding product. And it is for this reason alone, I did not give this product 5 stars.

I have now had my unit repaired, and am happy to report that it is working well. I have tested it on an 1800 mile drive, and it stayed on all the time and even appears to produce reasonably correct predictions of fuel economy. Had it worked like this the first time, I would probably have rated it 4 or 5 stars.
A word of advice, however: If you buy this product to save gas in your vehicle, you need to realize it is really all about you being willing to change your driving habits, and not about the Scangauge II doing it for you. In other words, you need to really commit to keeping an eye on it and changing your driving pattern to see any difference - otherwise, you will just have an expensive thing on your dashboard which confirms what you already know - that you are getting crappy mileage in your vehicle. Given the necessary adjustment, I still haven't gotten to the point where I trust the ScangaugeII more than I trust the math I can do when I fill up my car and divide the miles on the trip counter with the gallons I just put in the tank. Oh, and remember, for it to be accurate, it needs to be told EVERY time you fill up your vehicle, exactly how much you put in.