Turn Signal Malfunction

[pannoner3]

Hi all,

I encountered a weird issue tonight with my 21 Yukon SLT. Got a message on the dash to check front left turn signal, and when I got out of the truck it was illuminated solid orange. This remained illuminated even after shutting it off and locking it. I also noticed the headlight assembly has moisture on the inner part of the glass. Was going to bring it to a dealer, but figured I'd see if anyone here has encountered this before and knows a solution.

 

[Joseph Garcia]

Wow! That's a lot of condensation. I would remove the light assembly, dry in out, and look for the point of entry for the water, as it may be easily fixable.

While you've got the assembly out, inspect all of the bulb sockets and look for water-related corrosion on the contacts. This may be the cause of the light's odd functioning.

 

[pannoner3]

Thanks. I've been trying to find some resources for how to remove the headlight assembly. Seems the front bumper needs to come off, but I could be wrong. Interested if anyone can point me in the right direction.

 

[EvergreenZ71]

Thanks. I've been trying to find some resources for how to remove the headlight assembly. Seems the front bumper needs to come off, but I could be wrong. Interested if anyone can point me in the right direction.

Sounds right.

I think the Germans started that trend and stupid US engineers thought it was a good idea to make it harder for the average vehicle owner to even change their own light bulbs.

One of the backwards steps that happened between the NBS / 800 & the NNBS / 900; and GM never looked back. I’m actually surprised the aftermarket manufacturers didn’t explore how to do a headlight frame and pin-removed headlight in the newer trucks like the NBS had.

 

[SpareParts]

Na. Un hook the front of the wheel well liner and you can get to the 10mm headed bolt.

 

[jerry455]

There are no replacable bulbs on the new series trucks. The turn signal is LED. The fascia or bumper covers are not that hard to take off. I am sure someone here has done it or there is a youtube about it.

 

[pannoner3]

Sharing an update here. Decided to try and tackle this myself today. Bumper and headlight removal did prove to be easier than expected. The headlight with moisture inside had a significant amount of water pooled inside the bottom of the assembly, and I found evidence that the front bumper and headlight had been damaged and repaired at some point before I bought it (bondo, broken components, overspray, etc) though there's no accidents listed in the vehicle history.

For parts, the OEM headlight assembly is $1k+ or reman and aftermarket units are available for a wide range ($150-750). I went with cheap aftermarket, which seems to have been a mistake. Although they were a direct fit and installed without issue, there seems to be an issue in terms of compatibility. I immediately started getting the same error message as before: "Check Left Front Turn Lamp" along with faster than normal flashing signal lights. Other than that though, so far the headlight and turn signal are not getting "stuck on" after the truck is off as they were with the old unit with a moisture issue, which is an improvement. But obviously the error message and fast flashing are less than ideal.

At this point, I'm not sure if I should get an OEM headlight to see if that resolves the issue, or just live with these aftermarket units. Or is there a chance there's something else at play electrically?

 

[jfoj]

Spit balling a bit here. Not sure how difficult it would be to unplug the turn signal and then see how the flash speed behaves and if you get any specific errors. This is what I would try just to see what changes, if anything.

Guess 1 of 2 things will happen, flash speed and error will not change or flash speed may change without error or a different error.

This may help determine if there is a BCM problem, assume the BCM controls the exterior lighting unless there is a specific light control module. I have not had a chance to get smart of this chassis, what modules control what functions.

 

[pannoner3]

Ya I can do that. Thanks for the suggestion. BCM was in my head as a possible issue, but with all the water in the bad headlight, I still think that's the culprit and I just bought bad aftermarket units off eBay cuz I'm cheap.

 

[jfoj]

Sometimes the lights need to load the BCM/LCM so it can determine if there is a functional bulb/LED an many aftermarket assemblies may not load the circuit properly??

 

[BigdawgR6]

Unrelated but this is the first time I've heard of anyone using an aftermarket headlight. How is the light output and quality compared to the OEM? Is it consistent with the other headlight? Just curious as I think the headlights on these rigs aren't that bright IMO.

 

[pannoner3]

I'll get some pictures to post, but they seemed maybe a bit brighter or more vibrant. Which is why I'm disappointed that it's throwing an error message on the dash.

 

[pannoner3]

Out driving in the truck now, and interestingly enough, when I turn the hazard flashers on, the signal lights flash normal and no errors appear in the instrument cluster. So it's something specific to using the turn signals independently it seems?

 

[pannoner3]

Sharing an update here. I had my local GMC dealer attempt to diagnose this but they weren't able to come to a definitive conclusion. They said it's either a bad BCM, a bad wiring harness, or the aftermarket headlights are not communicating data correctly. According to them, with the aftermarket lights installed and with a single turn signal on, the car doesn't know which of the front signal lights is on.

In order to confirm which it is, they'd need to swap in known-good headlights to see if the problem persists. Knowing I already handled install of the aftermarket headlights, they correctly assumed I wouldn't want to pay ~4 hours of diag. So instead I'm going to reinstall one of the original headlights that I still have to see if it eliminates the problem, thus confirming the aftermarket headlights are the culprit. Planning to do this next week at some point, and will update after.

 

[Bw1r3ed]

Has this been resolved? I just bought a 2019 that had the wire harness nicked from the factory. Similar problem to yours. The wires must have worked for many years and finally rusted through. Thought I would browse the forums to see if anyone was seeing similar issues.

 

[pannoner3]

I never got a chance to reinstall my oem headlight assemblies to narrow down the issue.