The little frost warning symbol

[ukgroucho]

In my old C6 (and my A4 before that) the little * frost warning symbol next to the external temp readout would be lit up at 4C or less.

Driving around today and I saw some different behaviour in the A6..
First it seems that Audi are being a bit more cautious 'cos I saw the * on at temps up to 5.5C.
But what was more puzzling was that I saw temps of 4.5C where the * was not lit up, but later on (as part of the same trip) it was on at 5.5C and lower.

I'm trying to figure out when and why the car decides to switch the * on, it seems that it's not just a simple "if the temp is less than X centigrade then light up the *"

Anyone got any ideas what it's using to decide when the * comes on.

[hopgop]

I would assume it's an intelligent system that remembers what the temperature dropped to, then decides if a frost had occurred, not then switching off until a rise sufficient to remove the risk of ice. then not activating until a drop low enough for the risk to reoccur. Hence the difference in activation temperatures. That's what I assume anyway!

[ukgroucho]

Yeah I thought about wondered if would be a bit optimistic to try to predict whether there had been a frost in a specific location when you're travelling along at whatever speed... you can easily drop into a frost hollow where the temperature profile is very different to the bit of moorland you just dropped off.

I also wondered about the GPS position - rural vs. town (towns tend to have less frost), it certainly uses that for the adaptive headlights..
Also the sunlight sensor...

[Doctle Odd]

I have no idea so I'll madly suggest it comes from the TA broadcasts.

[zollaf]

me, i stick my hand out of an open window at 40 mph. if my fingers turn blue then there is a good chance of frost.
rely on a gadget like that, which is measuring air temp above the road and at speed, and you are likely to come more of a cropper than going on good old fashioned 'its icy, slow the duck frown'.

[Kar Krazy]

We had a customer reject her brand new car after she took delivery because it didn't have a frost warning and she relied on it to tell her whether to put a blanket on her horse. She had chosen a lower spec car to save money but expected the same kit as in her last motor. We sent her a £2.50 thermometer to fix to the wall of the stable along with a reminder about her payments. Oh the joys of vehicle leasing!

[Doctle Odd]

Liked a spot of riding did she?

We had a customer reject her brand new car after she took delivery because it didn't have a frost warning and she relied on it to tell her whether to put a blanket on her horse. She had chosen a lower spec car to save money but expected the same kit as in her last motor. We sent her a £2.50 thermometer to fix to the wall of the stable along with a reminder about her payments. Oh the joys of vehicle leasing!