It's a relatively new "general diagnosis" fee that they've started to charge. Some have reported that they're even advising people of this charge for items that should be covered under warranty - for example diagnosing a battery or drive unit for potential replacement under the 8 year unlimited mile warranty. If they determine it's covered under warranty, no charge - if not, that will be $175.
My car is out of warranty, I get the general idea, and had it turned out to be some piece of hardware that failed or other physical repair or calibration or what have you, I'd have paid the diagnostic fee without much complaint. But I think it's a little much to ask me to pay $175 for them to diagnose a bug in their own firmware that they pushed to my car and had been present for months across multiple different versions (I'm skeptical it's a firmware bug at all, or that they did anything whatsoever to correct it - car left with the same firmware rev it went in with - but that's another conversation).