How do states use OBD II for emission inspections?

How do states use OBD II for emission inspections?  - Emission inspection readiness - Maintaining your car - Maintenance and specifications - Volvo XC60 Owners Manual - Volvo XC60

Many states connect a computer directly to a vehicle's OBD II system. The inspector can then read "faults." In some states, this type of inspection has replaced the tailpipe emission test.

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