How do states use OBD II for emission inspections?

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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Electrical system
General information
12 volt system with a voltage-regulated alternator. Single pole system in which
the chassis and engine block are used as conductors. The negative terminal is connected
to the ...
Indicator and warning symbols
Low oil
pressure
If the light comes on while driving, stop the
vehicle, stop the engine immediately, and
check the engine oil level. If the oil level is normal
and the light stays on after ...
Emission inspection readiness
What is an Onboard Diagnostic System
(OBD II)?
OBD II is part of your vehicle's computerized
engine management system. It stores diagnostic
information about your vehicle's emission
controls. It ...
