Unruly Headlights

BuffettTruck

Well-Known Member
2005 Tahoe

Two weeks ago, I swapped out the blown incandescent bulbs in my dash cluster for LEDs. Right after this, perhaps just coincidentally, a few things happened. First my headlights would come on or turn off at random times, but only during the day. This started happening almost the day after the led swap. The next thing that happened is that I noticed my voltage was sitting around 11 volts. Hooking up an OBD2 confirmed that my voltage was fluctuating between 11.4 and 12.9. After stopping at Autozone, it was confirmed that the alternator was shot as well as the battery (I am guessing the bad battery caused the alternator to burn itself out). After swapping out both, the headlight issue seems to maybe slowed down, but it still happens. Sometimes just putting the key into ACC position will cause the lights to come on. But, again, only during the day. There is nothing on the dash and nothing on the daylight sensor (I really had to look because we just went through lovebug season here in Florida and those suckers get everywhere.) I am just spitballing, but I think it is probably an issue with the relay for the auto headlights, but that begs the question as to why the issue only happens at night? If the relay were bad, wouldn't that affect night time usage as well? I also keep wondering if maybe if somehow the LED swap has anything to do with it, but that just doesn't make sense to me at all.

Any insights?
 

Blckshdw

Moderator
When you took your modules out, to swap in the LEDs, were you anywhere near where the daylight sensor plug is located? Could it be possible that you strained the wiring and a pin could be loose, and making intermittent contact, so it's getting variable readings when it shouldn't be? Another way you could test it, is to unplug the sensor, and see if the behavior changes at all. Could be it just went bad?
 
OP
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BuffettTruck

BuffettTruck

Well-Known Member
I don't think so. I can pull my cluster out again and look to see how the sensor cable runs, but I didn't mess with anything other than the cluster harness and even with that I was as gentle as I could be.
 

Blckshdw

Moderator
Either way, I'd start troubleshooting at the sensor. Maybe put a piece of tape over it, and see if the odd behavior stops happening during the daytime.
 

TJBaker57

Well-Known Member
Got the Torque Pro App and a cheap elm327 clone?? If so you can check the light sensor volts straight away from Torque Pro!

 
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BuffettTruck

BuffettTruck

Well-Known Member
Thanks for that PID. I'll plug it in to Torque and see if I get a reading tomorrow if the lights come on.
 

TJBaker57

Well-Known Member
Thanks for that PID. I'll plug it in to Torque and see if I get a reading tomorrow if the lights come on.
Though I developed the PID in an 02 Trailblazer 4.2l I just confirmed the light sensor PID works in my 2005 Yukon 5.3l as well so you should be good with your Tahoe. Higher voltage equals less light. Just after sunset I had 4.7, shined a pocket flashlight at the sensor (center dash) through the windshield and dropped to 1.2 volts.

Edit: I think you get a reading regardless of whether the lights come on or not
 

TJBaker57

Well-Known Member
Another PID that may be worth a look is the 'Low Beam Duty Cycle'. Although you mentioned sometimes the lights come on just by turning the key to Acc. The DRL system doesn't turn on the headlights if the transmission is in Park. Or at least this is what the manuals state and I confirmed this with both my 02 Trailblazer and my 05 Yukon. Seems unlikely you had the key to Acc when not in Park.

On my Trailblazer I was able to get 2 values for duty cycle, 100% and 82% using a flashlight on the sensor in the dark. On the Yukon I was unable to get any sort of reduced output, only 0% or 100% with the flashlight trick.

PID = 222124
Name = Low Beam Duty Cycle
Short Name = DRL Duty
Units = %
Scale = x1
Equation = (A/255)*100
Header = 6C40F1
 
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BuffettTruck

BuffettTruck

Well-Known Member
This morning, Torque read 4.7v while taking the kids to school. On the way back home the sun came over the trees and the voltage started dropping and when it hit 3.8-9, the lights went out. An hour later I ran a load to the dump and the meter read 1.3V under a clouded sun. As I approached the dump, the dashlights came on and Torque read 4.7V again. I left the Tahoe running as I unloaded and when I got back in it was back down to 1.2V. On the way back home it jumped back up to 4.7V and for the last 5 mins of the drive the voltage slowly dropped to 4.1V, 4.0 when I stopped in the driveway. So I will pull the cluster and radio out and see if there is a loose connection and may even try running a cotton swab with a tiny amount of cleaner over the sensor's lens.
 

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