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:
Power brakes function only when the engine is running
The power brakes utilize vacuum pressure
which is only created when the engine is running.
Never let the vehicle roll to a stop with the
engine switched off.
If the power brakes are not working, ...
Acceleration
The air conditioning is momentarily disengaged
during full-throttle acceleration. ...
Recalibrating TPMS (Canadian models only)
In certain cases, it may be necessary to recalibrate
TPMS to conform to Volvo's recommended
tire inflation pressures (see the inflation pressure table on page 291), for
example,
if higher infl ...
