Daylight dash lights intermittent

WALLIES

MEMBER
2006 CADILLAC DEVILLE DTS
V8
FWD
AUTOMATIC
30,000 MILES

I keep the dash lights turned low for night driving. About 2/3 of the time when I drive in daylight the dash brightens up (brighter than it can be adjusted with the switch). The other 1/3 of the time it stays nearly black during daylight hours. I turn it up and drive it, but can't see it as well as I should. Then sometimes during the trip, it will suddenly brighten up into the daylight mode. Or sometimes it is the opposite; I start out and it is fine and later will suddenly become dark. Is there a daylight sensor somewhere that is possibly dirty or defective?

Tuesday, March 16th, 2010 AT 4:52 PM

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

If the brightness is changing on its own and you are not touching the switch then yes, that is most likely going to be a sun load sensor.

The way this works is the sensor is there to tell the body control module what the ambient light is so that it can adjust the brightness accordingly.

This means we need to start with checking to see if we have a complete circuit on this signal wire to find out if the BCM is getting the proper signal or not.

https://www.2carpros.com/articles/how-to-check-wiring

Basically, depending on the ambient light condition, the voltage is going to vary so we need to use a flashlight while monitoring the voltage and make sure it changes when you shine the light on it.

If it does, then the BCM is likely the issue.

I am attaching the wiring diagram below which will help with determining if there is an issue with this.

Please run through this and let me know what questions you have.

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