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:
From outside the vehicle
The remote key locks and unlocks all of the
doors and the tailgate.
Before the vehicle can be locked from the outside
with the remote key, the driver's door must
be closed. Any other door/tailg ...
Safety
Volvo’s Roll Stability Control System employs a gyrosensor. If the rollover
risk reaches a specified threshold, Dynamic Stability Traction Control is
activated. Inflatable side curtain-type airbag ...
Using HDC
HDC allows the car to roll forward at a maximum
speed of 6 mph (10 km/h), and 4 mph
(7 km/h) in reverse. However, the accelerator
pedal can be used to select any speed that is
possible in firs ...
