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Ice Warning

Rob writes:

"Alberto SCHILEO, DCC/USD" <Alberto.SCHILEO@domain.elided> writes:

>>BTW, has anyone seen the "black ice sensors" that SAAB used to have?
>
>    my 328is does it via the OBC.  When it detects an exterior temp of 2 or 3 
>degrees celsius under the fender (I do not remember which is the treshold) it 
>will gong, and display the outside temp to alert you that it's probably icy on 
>the road.

I would phrase that as "possibly icy on the road."  The gong sounds
almost
every time I drive during the Midwestern winter, yet there is very
rarely
ice on the road--the OBC cannot know if the road is wet.  Even if you
see
for yourself that the road is wet, you have to evaluate whether the salt
on the road (where I live, anyway) has depressed the freezing point of
water
enough to eliminate the possibility of ice forming.

The warning is almost useless for the conditions I drive under, but I
suppose
it could be more valuable in other parts of the world.

Rob
opus64@domain.elided


My understanding is that an alarm warning ("gong") will sound whenever
the temperature drops to 3 degrees celcius (about 38 F?) and this has
nothing to do with ice detection.  Rather, it is just a warning that the
conditions (i.e., temperature) under which ice may form now exists. 
Although the air temperature may be 3 degrees C, the road temperature
may be closer to 0 degrees C (say, the road over a bridge) -- the
temperature when water freezes.

As I recall, there is no "gong" when the temperature increases to 3
degrees C, which makes sense since no warning should be necessary.

Regards,

Steve