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I used to have a car (2011 Toyota Yaris) that had electronic headlight level adjustment with a knob on the dashboard. However, my 2016 Toyota RAV4 hybrid apparently has automatic adjustment, so there's no knob.

How can this automatic adjustment work? I mean, if it's based on gravity, the lights would be completely incorrectly adjusted if driving up or down a hill.

Is there some kind of level measurements in all four springs of the car, allowing knowing how much load the back wheels and the front wheels have?

If the automatic headlight level adjustment was non-operating for some reason, what could the cause be?

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On some cars there is a sliding reference mechanism on the front suspension to recognise how much weight is added to the car behind the front wheels (as the front weight is effectively constant) - that is then used to drive the headlamp adjuster motors appropriately up or down.

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  • Ah, that makes sense! Didn't think of the front weight being constant, but I guess it is nearly constant, when you think about it. Load on the back of the car is definitely the reason why these headlight adjusters are needed.
    – juhist
    Commented Jul 26, 2017 at 20:46
  • And some vehicles has that mechanism on rear suspension, similar mechanism is also used to adjust rear braking pressures on some vehicles.
    – Sampo Sarrala
    Commented Jul 26, 2017 at 21:49
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As far as I know, they work just as you surmised. A sensor detects the angle of the car body and electric motors adjust the headlights up or down to compensate.

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  • But how does it compensate for the angle of the road? Wouldn't this mean that the lights are always trying to aim at the horizon?
    – raydowe
    Commented Sep 25, 2017 at 8:17
  • The angle of the car body isn't going to change much with the angle of the road. Cars are heavy. If I punch it in my MINI, I can see the headlights adjust down because the angle of the car body has shifted (in this case, the front has lifted due to the acceleration).
    – Spivonious
    Commented Sep 25, 2017 at 13:49
  • Ah, I see. I took that to mean the angle of the car body compared to the horizon, not compared to the road. It must be using sensors on the suspension then, instead of using a gyroscope or gravity.
    – raydowe
    Commented Sep 26, 2017 at 7:34

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