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:
Marker lines
The PAC system's lines
1 Marker line for a 1-foot (30-centimeter)
zone behind the vehicle
2 Marker line for the clear back-up zone
3 "Wheel tracks"
The solid line (1) indicates a zon ...
System
The formats supported by the system are:
Advanced system settings
These settings can only be made when there is
no disc in the CD/DVD player.
- Press MEDIA MENU.
...
