What Is a Diagnostic Test for a Car?

Diagnostic tests are used to determine what repairs are required to ensure a vehicle operates properly. On newer model vehicles, an on-board diagnostics computer interface is used in conjunction with diagnostic tools and software to help mechanics identify problems.

The diagnostic test is performed using a scanner that is inserted into a special connector, sometimes found under the dash on the driver's side of the vehicle. The scanner receives information regarding the vehicle's model, identification number and engine type. It also receives and identifies a specific diagnostic code that relates to a specific problem. The diagnostic test and code helps the mechanic understand where to look to make the necessary repairs.