This is the code reader that GM used until 1994. You can access computer areas that other code readers cant, and you can get readings at real time, as they occur. Another benefit of the Vetronix Tech 1A is that it will do a diagnostic circuit test, scanning the entire system including the circuitry. With this code reader you can also make checks and changes to identify that systems are operating properly. This reader definitely gives the home mechanic all of the information he needs, and more.