How OBD II Works-Monitors

Several new tests, called monitors, are used with OBD II. Monitors are tests that are programmed into each OBD II vehicle computer. Monitors test the vehicle for things like engine misfire, excessive fuel system corrections, catalytic converter failure, and other conditions that may cause an increase in harmful vehicle emissions.

Some OBD II Monitors are found in all OBD II vehicles. Others will be used in some—but not all—OBD II vehicles, depending on vehicle make, model, year, and emission system design.