The “just plug in my car for diagnosis” folk tale
This myth has grown for many years. While connecting a diagnostic computer to your vehicle’s computer(s) is a crucial part of many diagnostic procedures, doing this will not tell the technician what is wrong; it only points to the area of the problem.
“Just hook my car up to the computer” myth I suspect, came from car manufacturers and salesmen who wanted to brag about their technology and how it makes their cars easy to fix. Diagnostic information accessed from your vehicle’s computer is often vital to solve driveability concerns but additional tests are required to confirm which component of the system is actually faulty.
For example, when your check engine lamp comes on, the trouble codes generated and the data available on the scan tool/diagnostic computer, is the information that the vehicle’s computer generates based on the information that it receives from numerous sensors.
Let’s say the code is for an oxygen sensor defect; the vehicle’s computer has no way of knowing if the sensor is reading correctly, a wire to the sensor has broken or the computer itself has an internal defect. From the information gathered on the diagnostic computer very specific tests must be conducted and this is where a technician’s skill, resources and other diagnostic equipment come into play to find the real problem.
So forget the “plug it in for diagnosis” myth; more thorough tests are always required to be certain to find the real cause of the concern.