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:
CHANGE CODE
This function makes it possible to change the
channel access code. The default code is
0000.
To change the code:
1. Select CHANGE CODE and press
ENTER.
2. Enter the current code and press ENTE ...
Setting a warning distance
This setting determines the distance at which
the visual and audible warnings are triggered.
Select Long, Normal or Short by pressing MY
CAR on the center console control panel and
going to Set ...
Engine compartment
1 Engine compartment, upper
2 Engine compartment, front
3 Engine compartment, lower
Positions
These fuses are all located in the engine compartment
box. Fuses in C are located under A.
NOTE
...
