Fog Light Behavior When Using Automatic High Beam Mode

I like the look of fog lights on a car (probably due to not having owned a car with fog lights for much of my life). I never considered buying anything but the Touring version when I was shopping for a new Prius, even though I realize (as has been covered here in another thread) that the lights do little to improve visibility even in conditions (fog) for which they were designed to be used.

Now I read in the manual (page 253) that "Fog lights can be used when: The headlights are on in low beam." I had been leaving the fog light switch in the "On" position all the time, but now I'm wondering, do they really switch off when the high beams come on, particularly when in Automatic High Beam mode, since in that mode the high beams can switch on and off multiple times within a short period of time? If the fog lights do switch on and off as the high beams switch off and on, would this cause either the bulbs or circuits to burn out prematurely? For now I've been leaving my fog light switch in the "Off" position, but then what's the point of having them? Do I need to stop using the Automatic High Beam mode if I want to use my fog lights?

 

Wow, I never considered the possibility that driving with them continually is illegal. I wonder if that is really true in North America. I see plenty of people who do seem to have them on in all kinds of conditions, and in fact, on my 2007 Prius they come on automatically with my headlights. I'm not sure that was always the case. I recently had to replace one of the fog light bulbs that had burned out, and since then I've noticed they are on all the time, the fog light switch appears to do nothing. (Since I don't have DRLs on the 2007, and since the headlights turn off automaticalIy when the car powers down, I leave my headlight switch in the on position.)

Can anyone else comment on whether it is illegal in North America to drive with fog lights when there is no fog?

 

Good to know. I assume the Prius would meet the requirements. Now if only I knew whether they do switch off and on again each time the high beams go on and off and will this cause premature burn-out.

 

I was pretty sure they would turn off, if I manually turned on the high beams. Testing whether they turn on and off with auto high beams was a little harder to test, involving standing outside the car on a highway in the dark and watching how they behave as the high beams go on and off with approaching cars. I haven't tried that. I guess I might consider changing the sensitivity of the light meter controlling the auto high beams, or stop using them altogether, because I've noticed they will toggle on and off several times in a few seconds as cars approach and then pass by. That can't be very good for the headlights themselves, never mind the fog lights. It's nice to know the car has that kind of technology, but actually using it might be a bit of overkill.

 

Thanks for the info. So rather than having the high beams turned on and off electronically, there is actually a moving part that does the job? That makes me even less comfortable about letting the auto high beam unit take control, knowing that if I were in control I would be toggling them off and on much less frequently.

 

Thanks for pointing that out. I had seen it and when I talked about changing the sensitivity of the light meter, I was thinking of using that procedure.

It's interesting to me that this kind of "cheat" is written right into the manual. It's the type of knowledge that might be used to gain an advantage in a video game, say, but would not normally be disseminated to everyone. It kind of makes me think it was added into the manual as an afterthought, especially since it appears it was not properly edited (in 4, "indicator is turn on and off 3 times")

 

I actually still have an '89 Supra that I take out occasionally. I was a long time member of the Supras group on Yahoo, and I remember one of the most popular mods that people were doing to those cars was to re-wire the fog lights, so they could be turned on independantly of the headlights.