external temperature WAY out

[Blown2CV]

Noticed recently on my W205 C-class that the external temperature reading is miles out. It was showing 19 degrees this morning when it was around 5 degrees outside. I also saw it recently jump up 20 degrees or so, and then gradually return to the approx accurate reading. I know these things are not exactly bang accurate normally, but this is a massive change to normal. What is the impact? Is it just for driver info or does it affect how the car operates?

[DKL]

I'd be inclined to find the sensor at the front and remove/clean/refit.
My e55 suddenly said about -5 in the middle of last summer. The sensor was in one of the vents under the headlights, I imagine they all are, and if was very loose. Quick clean and refit fixed it.
No idea if it affects anything else, I'd doubt it.

[Blown2CV]

having thought about it, it did have some bodywork done a few months ago - likely the sensor didn't get refitted properly or they've fked it.

[PositronicRay]

I don't think it'll effect the running of the car. You'll have a separate air intake temp sensor for engine management.

[TarquinMX5]

It can affect some things such as heated mirrors etc. and I *think* all MBs work this way, certainly mine do, as did previous ones.