Consumer Repair Guide
If a technician just hooks my car up to a computer that spits out the problem, why should I pay for that?
It doesn't quite work that way. A diagnostic computer is typically a handheld device that plugs into a service port on the car and allows the technician to view the same data that the computer accesses. The diagnosis does not pop up on the screen, however. The technician must read voltages, vacuum readings, and other data to determine which parts are operating correctly. Is a sensor not operating? Or is the connection bad? If a system is failing, the computer will store a code that helps the technician find the root cause of the problem.
Vehicle repair without computer diagnostics is based on an educated guess. Technicians rely on computer diagnostics just as doctors analyze medical test results before performing surgery. Like doctors, they must have the training and experience to interpret the data delivered by sophisticated tests.