My 2015 VW Golf has the fancy lighting system with the pointable HID headlights (I leave it off; it really distracts me when the light beam doesn't point where the car's going). For quite a while I've had an "Error: Adaptive Front Lighting (AFS)" warning pop up, but the headlights seem fine (and still do their usual wiggle when I start the car).
I finally did some googling, and apparently this indicates a bulb problem, probably with one of these side-illumination light bulbs:
Clearly these are supposed to light up when turning, and it makes sense that one could be out and I wouldn't notice. I have no problem with how the lights are currently functioning, but I do want that error message to go away, and would be willing to replace a bulb or two to make it do so. But, here's the problem: neither of these lights EVER seems to turn on (at least while parked with engine running and headlights on). I've turned the wheel all the way, turned on the turn signals: nothing. I'd rather not blindly replace bulbs, hoping to get the right one.
So, finally: the question. Under what circumstances are those two lights supposed to light up?
Final Edit: I pulled the two bulbs, and found that the left cornering bulb had failed (the right bulb was good, even though it never turned on). I've replaced the failed bulb (it's a standard H7 halogen); the error message has gone away, and now both bulbs work. See my answer below for the details.
(and no, this isn't the only reason...)