See also:

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 ...

External audio source volume
If an external devices such as an MP3 player or an iPod is connected to the AUX socket, the device's volume may be different from the volume of the internal sound sources such as the disc play ...

Limitations
Even if a fairly small section of the screen image appears to be obstructed, this may mean that a relatively large area behind the vehicle is hidden and objects there may not be detected until ...