Programmers can be either plug-and-play or an external device. For the first type, you need to plug it into the OBD-II port of your vehicle. The tuner gets all the information from your vehicle’s computer system. This computer system pulls the customized tuning from the programmer.
The external type of tuners is not connected to the vehicle’s computer system but is connected to the wiring harness of your vehicle. It’s a stand-alone computer by itself. These catch signals from engine sensors and sends the modified signals back.