Vehicle diagnostics are the mechanics involved with identifying and assessing problems that may negatively affect the normal operation of a vehicle. Mechanics may employ a wide range of techniques and tools in conducting vehicle diagnostics, ranging from cursory physical checks to more involved, computer-based analysis. Given the sometimes occult nature of mechanical problems, effective diagnostics are critical to successful repairs and the smooth running of any vehicle.
Historically, effective vehicle diagnostics relied on the individual competence of a mechanic, in his being able to use visual or audible clues to correctly assess a vehicle malfunction. Symptoms of a mechanical problem can range from the obvious, such as oil leaking from a faulty seal, to the indirect, such as rough engine idling. Prior to the integration of computer systems in vehicles, mechanics often had to be equal parts detective and surgeon in putting together clues to diagnose and fix problems.
With the advent of electronic control units (ECUs) in cars, airplanes, boats, and motorcycles, however, the task of vehicle diagnostics has become markedly simpler. Through the use of ECUs, technicians can take advantage of computer technology to aid them in identifying and resolving malfunctions. Virtually all modern road vehicles now come equipped with onboard diagnostics (OBD) ports, which work with the ECU to monitor various sensors throughout the vehicle, and log codes when errors or problems are encountered.
Tied to a vehicle's dashboard or information screen, an ECU can alert the operator when it detects a malfunction by displaying a check engine or malfunction indicator light (MIL) warning. Anyone with a special cable and laptop can literally plug into a vehicle's OBD port and download the error codes to determine exactly what is wrong. OBD ports have greatly expanded the scope of who can perform basic vehicle diagnostics, and many general and automotive parts stores now charge a nominal fee to scan an OBD port and interpret the error codes.
Knowing what is wrong, however, is still only half the battle. An experienced mechanic is still crucial to resolving malfunctions, and there are still many mechanical problems that can occur without triggering an error log by the ECU. Vague rattles and other noises, inexplicable loss in fuel efficiency, and steering that pulls to one side or another are all examples of operator complaints that may not be recorded by the computer, but can be further investigated and successfully resolved by a skilled professional.