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OBD II Basics
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How OBD II Works
Monitors are groups of tests that may be programmed into a vehicle's OBD II computer.

OBD II monitors test the vehicle for things like engine misfire, excessive fuel system corrections, catalytic converter performance and other conditions that may cause an increase in harmful vehicle emissions.

Not all monitors are found in all OBD II vehicles. The monitors not used in a vehicle will be reported on the Vehicle Inspection Report (VIR) as "Not Supported."
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