by the OBD port. I have an expensive Bluetooth unit that has a lot more capability and features. The more expensive one also has more manufacturer limits built into it. There are some issues that it won't let you reset the error codes for. Also, the Bluetooth unit takes longer to spin up, run a diagnostics, and connect to your phone by a significant amount. 95% Of the time I just use the $15 cheap scanner because it's easier to use and it gets the job done.

My most common issue, because I live at the end of 2 miles of gravel road, is a check engine light for a stuck evaporative vent valve. The dust from the gravel road gums up the actuator that opens and closes the valve, leading to a check engine light. Other than some gasoline fumes that might be escaping into the atmosphere, it doesn't affect the performance of the vehicle, so I will turn it off. The cheap units work well for that. If I'm doing some more technical troubleshooting, I'll use a more expensive advanced unit