The main difference between a hand held OBD-II tool and a scan tool is that scan tools are capable of retrieving more live data parameters that can open a larger window to figuring out the cause. That's great, but at a cost of anywhere from $500 to several thousand dollars, you're really opening your wallet. And, aftermarket scan tools still only give you about 75 percent of the OE data, and usually require that you purchase software updates to this manufacturer-specific information.
I know that's a lot of info, but the bottom line is an OBD-II reader is a must for anybody who wants to handle their own diagnostics, but that's as far technologically as most of us need to go. The next level scan tool is just too pricey for somebody who is only in charge of a few cars in their "personal fleet." There are some excellent readers out there for around 100 bucks! This reader from CanOBD2 does most of what you need, and you can't beat the price or the realiability you get from a company like CanOBD2 that specializes in modern automotive diagnostics.