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.
See also:
Current speed in mph (Canadian models only)
This function provides the driver with an instantaneous
conversion of the car's current speed
from km/h to mph. ...
Crash mode
Crash mode ...
Three-way catalytic converter
• Keep your engine properly tuned. Certain
engine malfunctions, particularly involving
the electrical, fuel or distributor ignition
systems, may cause unusually high threeway
catalytic convert ...
