Your vehicle performs up to 11 diagnostic checks of specific emission control components such as engine, transmission, fuel systems and other emissions controls. Each diagnostic check communicates with a monitor called a readiness monitor. These diagnostic checks are performed while the vehicle is driven. Certain driving conditions must be met to determine if all components are functioning within allowable standards. If all diagnostic checks have been performed, the computer reports systems as “ready.” If diagnostic data has been erased during vehicle repairs or through battery disconnection the computer reports systems as “incomplete” or “not ready.” Vehicles are rejected from testing when these diagnostic checks are not completed. This sophisticated system serves as an early indicator of exceeding the vehicle emissions standards, increasing air pollution emissions and of potential engine damage.
The OBD (On Board Diagnostic) system is more like a computer monitoring system. An OBD monitor is a computer test or series of computer tests used to determine if an emission control device or system is failing. The vehicle performs the self-diagnostic computer test when the vehicle is driven. This is commonly referred to as a “drive cycle.”