I have three vehicles with OBDII diagnostic ports. I carry an inexpensive scan tool adapter in each, such as:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
This thing plugs into the diagnostic port under the dash and creates it's own wifi signal. With the app installed on my iPhone, I plug in the adapter (key on, motor off), join the wifi channel and open the app. I can read and clear all codes, or use the phone as an extended instrument, with real time readings of temps, rpm, etc.
It helps greatly in making decisions when out on the road, ie, can I make it home or not?