Dash Lights Really Bright At Startup

[kevinkar]

Also posted on VWVortex....

2018 R, about 5 years old, no real problems so far. But, in the last 3 weeks I've gotten into the car in my dark garage and the dash and infotainment were really bright. A lot brighter than I had the brightness set to. So, on the way to work, I adjusted the scroll wheel up and down thinking maybe it has gotten a bit dirty or corroded and the brightness did go up and down but I got it set back to where I like it. Was fine for the 3 weeks but this morning the same thing happened.

This time I just left it alone and, within about 5 minutes the brightness dimmed down to where it should be without my adjusting it where it stayed until I got to work and shut the car off. Leaving work this afternoon the dash and infotainment screens looked normal to me.

So, anyone have phantom brightness adjustments happen which raises the brightness to a high or full value only to have it settle down back to normal on its own in a few minutes?

I ran an OBD11 scan but no faults were present. So just a glitch maybe though it hasn't happened in the 5 years I've had it since new until now, twice within the last 3 weeks. Weird.

 

[The Fed]

Not that issue, but I do have other occasional weird glitches. I've started paying attention to solar storms.

 

[Cuzoe]

Long shot but is the dashboard dusty? There's a light sensor in there.

Although as I think through it, a dirty dash would probably cause the opposite problem. Where everything would not get bright enough.

I would not expect that roller is the issue, but if you really want to test it, there is an adaptation you can change in the BCM that will move that brightness adjustment to a slider in the infotainment instead of the roller.

Change it to the slider for a while and see if the issue ever pops up again.

 

[Cuzoe]

https://www.golfmk7.com/forums/inde...ient-light-dimming.381530/page-2#post-7933788

 

[kevinkar]

Thanks Cuzoe. No, the dashboard is clean and that was one of the first things I checked but everything seems OK in the cleanliness regard. As for the adaptation, that's a good suggestion so I'll try that tomorrow as I did notice when I first experienced this a few weeks ago, small rotations of the wheel seemed to produce large changes in brightness so maybe that's just a bit dirty/corroded and I'll have to see how hard it is to get that out and get some emery cloth to clean off contacts or maybe get some contact cleaner sprayed into it (hmmm, long run-on sentence there.) But if the slider tweak works, that would be fine by me.

 

[Al_in_Philly]

If it is a dirty or corroded potentiometer, the "old school" quick-fix would be to roll it back and forth about a dozen times to scrape off whatever is coating the contacts. Otherwise, you'll need to pull out the unit and spray some contact cleaner into the guts of the pot--usually where the rotating shaft enters the main body, as usually they are fully sealed units. If you do that, just use plenty of contact cleaner and let the potentiometer sit for a while on top of something like an old newspaper to allow whatever excess fluid to drain out.

 

[kevinkar]

If it is a dirty or corroded potentiometer, the "old school" quick-fix would be to roll it back and forth about a dozen times to scrape off whatever is coating the contacts.

Yep, that's what I did on the drive to work the first time. Seemed to work but clearly it wasn't the solution since it just happened again. I guess I could try it again for more spins before I spray it.

 

[kevinkar]

Made Cuzoe's change to get the lighting in the infotainment and it was already showing "low" so I moved it up and down back to low and left it there. I also see the setting changing the potentiometer to "not installed" resulted in the wheel not being effective anymore so no instant changing for the time being if it's too dark or bright. But, with it set to low in the infotainment and the scroll wheel ineffective, that should point to it as a culprit if it doesn't change brightness in the next few weeks. Though I'm not sure that's actually conclusive one way or the other. Definitely not a problem if the brightness changes on its own again.

Also checked the battery (12.3V after sitting there overnight) and alternator (putting out 14.3V at the battery) so I don't see anything wrong there. And the light sensor was definitely clean.

So, right now it's a gremlin and I'll see if the deactivation of the scroll wheel has any effect.

 

[The Fed]

Is there actually a potentiometer that directly controls the brightness, or does it tell a light module to vary the voltage to the dash lights? Just a thought.

 

[kevinkar]

Is there actually a potentiometer that directly controls the brightness, or does it tell a light module to vary the voltage to the dash lights? Just a thought.

Without any electronics diagram, I don't think you can tell. The scroll wheel has end points unlike the volume control which just spins infinitely so I'm assuming it's a standard pot but can't really tell.

 

[Cuzoe]

@The Fed and @kevinkar It's a little of both. It is a potentiometer, but its value is provided to the BCM. BCM takes that input along with many other things and varies the brightness... of many things.

One of those things is the dash brightness, but the dash brightness is also influenced by the light sensor in the dash.

One of those things is the brightness of the hazard button. But it's worth noting the hazard button is connected to a dedicated light channel of the BCM and that channel can be set to a maximum and minimum brightness. So in that instance, the input from the pot is mapped to a max/min of the light channel setting which is also varied by some other inputs, including whether or not your headlights are turned on and whether any of the impact sensors have been triggered.

Another thing is the white background button brightness. Dozens of adaptation channels that determine the max and men brightness, and the dimming curve of those lights. You control where you are on that curve via the potentiometer.

Another is the brightness of orange lights in the car, so your lock/unlock, your window lock. These are again mapped to dozens of BCM channels that determine their max/min brightness and curves. And just like the white background lights, the value of the pot is then mapped to somewhere on the curve that was created by those adaptation channels.

It's all very simple . What it ultimately allows for is a single module type, like the BCM, to be used across dozens of models and properly manage interior light/display brightness across any number of different display types, background lighting colors, background light types (LED vs Incandescent, although those are mostly going away).

The BCM solution allows you to have one control point that manages the brightness of everything in the car. Some things will of course have limits, for example, you can dim the white background lighting very low, but there's a minimum brightness that the digital cluster will always have, assuming factory settings where you haven't messed with the adaptations. And then of course some things like the infotainment screen have their own setting that establishes a baseline that is then adjusted via the BCM/ potentiometer.

 

[Cuzoe]

As we meander on and off topic, some very cool work being done by a member over on Ross Tech to setup, as much as possible, a night drive mode that practically blacks out all the background lighting in the car except what you need to drive.
https://forums.ross-tech.com/index.php?threads/40023/

They are recreating the "Night Panel" mode that some Saabs came with...

 

[The Fed]

I forgot about the dash ambient light sensor.

 

[kevinkar]

Maybe you're short and can't see it way up on the dash? Heh heh.

So far no weirdness since I made the change to the control now being via the infotainment. Since I set it and forgot it back in 2018 and it seems to be the level I want it to be I should never have to touch it again anyway so, if it happens again, I guess it's just a gremlin.