By now we all know how to disable Care Mode from running automatically (Car Mode>More>Settings>My Cars>Unclick Auto Open). That worked perfectly with my GPS.
To my dismay, I discovered that Car Mode ran automatically when I was in the car with my other GPS. Even though it had been previously Bluetooth connected to the phone and successfully used, somehow that GPS was not listed in My Cars as a Registered Car, but Car Mode auto ran anyway. Once I got that second GPS to appear in Registered Cars, Car Mode no longer ran when that GPS was powered up and linked to the Galaxy S5.