Screen brightness goes up & down, have to turn it off at night

I'm having to turn off the screen when I drive at night to avoid the distraction of it weirdly and endlessly jumping up and down in brightness. It happens when I turn down the brightness of the dashboard instrument cluster to an intermediate level. With the instruments at max, the screen brightness is constant. With the instruments turned off completely, then too the screen is fine. But neither of those settings is safe at night. I don't want to drive without a speedometer, and I don't want to drive with the instruments brightly reflecting in the windshield. Any of you know what's the cause and/or fix of this thing with the screen? I'd love to know! I suppose I'll be having to pay the dealer or somebody to fix it, but I'd rather not go in clueless--and I suppose being clueless, it could be something simple I'm just overlooking. Thanks for any thoughts. BTW, this is re: our 2008 Prius, options package 4

 

Interesting about that warranty. Superficially it seems to be about something different, but my car's problem clearly has _something_ to do with combo meter, and although I didn't mention it, the combo meter might be weird in another way too: when I turn the knob to adjust the brightness, it doesn't happen gradually, because mostly as I turn it nothing happens, until at a certain point it jumps over just a few hairs of a turn, so it's impossible to adjust it exactly to an in-between brightness. Anyway, I guess I should find a mechanic to tell me if it's related to the warranty issue.

Does anybody else have a theory?

 

Are you talking about the screen brightness, instrument brightness control or both? I'm thinking most of this stuff is integrated circuits. Are there pots in there as individual elements?

 

Yes, a thumbwheel...according to the manual. We just bought the car and my wife is driving it. I don't think I've played with it myself yet.

 

Thanks so much! I wonder if fixing the pot/rheostat is likely to stop the slow periodic oscillation of the display screen bias. I suppose it might. How confident are you that a broken one of these is the cause of my thumbwheel weirdness? I'm guessing it's something you've seen before...?

 

You mean in mfds normally, or do you mean you thought that's what I was describing about my own mfd? I don't know if the headlights have anything to do with it. What I observe is that I dim the speedometer and as long as it's dim the mfd will jump back and forth in brightness--every 10-30 seconds or so (I haven't checked the interval or if it's strictly periodic). It's dark out when I've done this, so I suppose the headlights are on.

 

Awesome, xliderider! Thanks again!

 

I've never bought a part off eBay or done much in the way of repairs. I wonder if I could get that rheostat a lot cheaper at a Pick-n-Pull type (DIY salvage) place. Then I could get a little practice accessing the thing on a junker before taking a hammer to our new car.

 

It seems that version of the part with the number ending 2020 isn't right for my model year (2008) and that I need one ending 2030, at least according to these two sites:
Instrument Panel Dimmer Switch for 2008 Toyota Prius|84119-52030

2008 TOYOTA PRIUS Base 1.5L ELECTRIC/GAS Automatic CVT. #8411952030: Instrument Panel Dimmer Switch.