another guage cluster problem

[MonteJ]

My gauge cluster is dark and uncontrolable in the sun but work correctly in the dark.
The dimmer works at night but not in the sun. I don't even know where to start?

 

[MonteJ]

2007 Yukon Denali

 

[mikez71]

Did you try a new light sensor yet?

 

[Doubeleive]

Check the little plastic bubble in the front center of your dash if that fell in the dash that could the problem, also be sure nothing is blocking the sensor on the drivers side forward facing part of the rear view mirror there is a sensor there also, if you installed say a dash cam or something right there it blocks the sensor it needs to be moved over to the right side of mirror

 

[MonteJ]

Check the little plastic bubble in the front center of your dash if that fell in the dash that could the problem, also be sure nothing is blocking the sensor on the drivers side forward facing part of the rear view mirror there is a sensor there also, if you installed say a dash cam or something right there it blocks the sensor it needs to be moved over to the right side of mirror

If the little bubble was not working how does it know when it is dark or not?

 

[Marky Dissod]

If the little bubble was not working how does it know when it is dark or not?

If the lil bubble is hidden or covered, it always thinks it's always dark.
Struggle to think of how it could wind up in a situation where it thinks it's always bright out ...

 

[mikez71]

If the lil bubble is hidden or covered, it always thinks it's always dark.

But why won't his dimmer work if it thinks it's dark all the time?

I have a hunch about nighttime modes, and and headlights/DRL's..
When it's night, and we turn the headlights off, the backlight dims to the lowest setting? (and becomes uncontrollable)
I occasionally get this issue some winter mornings where my backlight is dim for several seconds.
(My autoheadlights and DRL's have been tuned out though..)

If you ohm your ambient light sensor, here is what I found with mine.
The output ranges from 500ohms in direct sunlight, to 15k ohms fully covered.
BCM switches to night when resistance surpasses 5k ohms, and back to day when dropping below 3k ohms.
Sometimes, it takes several seconds to switch modes, so there are some other factors going on...
When switching instantly from 10k ohm to 1k ohm, the night backlight will go dark for 3 seconds before going daytime bright.
But going from 1k ohm to 10k ohm, the backlight dims instantly.

Below is the factory trick to bypass the sensor and get daytime backlighting, but it will also disable your auto headlamps..
Connect resistor between white wire and black or black/white wire depending on your HVAC setup.
You can just stick the resistor in the connector, but you might have to loop the ends so the connector can grab hold of it..
Don't let it fall into your defroster vent!

-----------PIT4328b--------------
Procedures to disable to auto headlamps:

Unplug the ambient light sensor and put a 600 ohm resistor in place of the sensor. The resistor willcommand the TBCM to turn the auto headlamps off. The headlights will now have to be manually turned onwith the headlight switch.Secure the resistor and connector to prevent rattles.etc.

Notie:Vehicles equipped with Automatic HVAC (RPO CJ2) may have a light sensor that also includes the sunloadsensor for the HVAC system. Make sure the resistor is wired into the ambient light sensor signal wire (Circuit 278)and ground (Circuit 1851). This can be achieved by backing out pin 2 at the light sensor and removing theterminal and adding the resistor to the wire and then splicing the other end of the resistor to the ground wire 2inches from the light sensor

 

[Doubeleive]

it should be noted that the cluster on the gmt900's is always lit during the day and the dimmer control works but just barely as it is hard to see it adjust at all.
if you take a piece of cardboard and block the outside light around the radio and adjust the dimmer you can see it adjust a little bit
that is normal operation during the day.
the op could be seeing normal operation
if you cover the sun sensor with a shirt or something during the day, then you will see the puddle lights come on when unlocking the doors if equipped and if lighting is enabled in the dic.
doing that will confirm the sunsensor is working
if you are in daylight without the sun sensor covered and the puddle lights come on then the sun sensor has a problem
same if the headlights are on in drive without the parking brake set during the day

 

[MonteJ]

If the lil bubble is hidden or covered, it always thinks it's always dark.
Struggle to think of how it could wind up in a situation where it thinks it's always bright out ...

Clarification: when it is covered the panel is visible and the dimmer switch works as it should.
When i pull in to the sun with it uncovered the panel goes "no lights".