Save money by having it diagnosed? Maybe, especially in this case. But save money by having them fix it? Almost never. You can usually buy the same parts cheaper elsewhere and you aren't paying labor. I had my alternator go out on a road trip.... $550 to replace a $150-200 part that I could've easily done myself if I had tools. The part alone was "$250." That doesn't include extra meals, tow (AAA membership in this case), hotel, etc.