Having a OBD2 bluetooth tool is fantastic, they are only $20 or so to get on ebay, the interface works on your mobile, with a free app.
Then you can see what error codes came up. Basically when you take it to a mechanic that's the first thing they will do.
The cars computer tells you what's wrong with it, all you need is that $20 part.
You can also keep an eye in real time of your boost pressures, coolant temp, etc, basically everything the car computer has info on.
i offered to put it in a friends car once as it had a warning light on the dash, she said nooooooooooooooo I need an auto professional.
Anyway the "Auto fkn professional" came around did the same test I would have done and found it was just a faulty brake light! WTF, why the maker would have a faulty brake light bring up an engine check light on the dash has me stuffed.
She paid a heap of cash just to have that diagnosed and fixed (dumbass).