Horn, cruise control and high mount brake light do not work

2015 GMC YUKON

37,000 MILES • 5.3L • V8 • 4WD • AUTOMATIC

MO-SAN

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31 POSTS
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I just brought the vehicle listed above SLT model. i found out, the horn when pushed on doesn’t sound out. I check the fuse and relay and all are in good working condition. I asked a mechanic friend to check it out with his diagnostic scan tool by testing the horn and it works fine with the scan tool but won’t sound when pushed on the steering and that’s a safety issue. Than comes the next issue with the 3rd brake light or the high mount light as some call It not coming on when the vehicle is in ignition, but will come on when ignition is off when brake paddle is depress. That tells me the LED bulbs are not bad. And it follows with the next issue finding out the cruise control won’t come on when driving above the 40 miles. I parked the vehicle and press on the cruise control bottom, it came up on the instrumental cluster, but when I tried driving above the 40 miles to set the cruise control speed, it won’t engage. The rest of the switches on the steering wheel work fine except the cruise control switches.
Will this issues have anything to do with a bad airbag Clock spring or any other switches towards the brake pedal?
I have also scan the vehicle and the below are some results on the scan reader.

Please advise what steps to take in changing any needed parts.

Thanks,
Mo

Image (Click to enlarge)

Sep 24, 2021 at 5:34 AM

JACOBANDNICKOLAS

CERTIFIED EXPERT
110,175 POSTS

Based on your description, it does sound like the clock spring may have failed. I looked through the schematics for the horn and CC and both use the clock spring.

As far as the 3rd brake light, it receives power directly from the body control module. Since it works with the key off, I'm questioning if there is a ground issue causing the ground path to be interrupted when the engine is on.

Try this. Pull the 3rd brake light out from the body. There will be a violet wire with a white tracer that supplies power to it. Using a test lamp and a known good ground, see if there is power to the light when the engine is on. If there is, check the black wire for continuity to ground with the engine off and again on.

Here is a link you may find helpful:

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

As far as the clock spring, I attached the directions for replacing it. See the pics below.

I hope this helps. Let me know if you have other questions.

Take care,

Joe

See pics below.

Images (Click to enlarge)

Sep 24, 2021 at 7:32 PM

MO-SAN

MEMBER
31 POSTS

Thanks a million Joe. Since I was so desperate in need of the car, I remove the airbag from the steering wheel to see if there are any lose wire connections but it all looks good. I decide to test the horn switches on the steering wheel by depressing it with a screwdriver and to my disbelief, they all work on all three location points. I look deep all around the airbag unit and to my disbelief again, I found all three plastic tabs that are supposed to engage with the horn switches on the steering wheel have been cut off. (What a shady car world we living in.) Please find attach three photos with screwdriver pointing to it. I guess I will be replacing an entire airbag for the horn and a clockspring to see if the Cruise control will work.
I will do as you said on the 3rd brake light issue and will report back any progress.
Again, thanks for assisting.
Mo

Images (Click to enlarge)

Sep 25, 2021 at 12:14 AM

JACOBANDNICKOLAS

CERTIFIED EXPERT
110,175 POSTS

Hi,

Did those break or were they cut? I've never seen them break like that before. Also, is the air bag light staying on? If it is, I'm wondering if the clock spring is an issue. Actually, if the horn works, I would think it's good.

Let me know.

Joe

Sep 25, 2021 at 7:35 PM

MO-SAN

MEMBER
31 POSTS

Hi Joe,

No, they weren’t broken, they seem to be cut off in all three locations. Airbag light doesn’t stay on. I just can’t understand it. The horn works when tested on the steering unit but won’t when the airbag is in place.
Since the Cruise control is also not working, I was hoping to change the Clock spring first to see what the outcome meant be. Thanks and will update again.

Mo

Sep 25, 2021 at 11:03 PM

JACOBANDNICKOLAS

CERTIFIED EXPERT
110,175 POSTS

I wonder if there was an issue with it sticking on and that was how they decided to fix it. I guess anything is possible.

Regardless, let me know if there is anything I can do to help.

Joe

Sep 25, 2021 at 11:07 PM

MO-SAN

MEMBER
31 POSTS

Thank you! Will do.

Mo

Sep 25, 2021 at 11:24 PM

MO-SAN

MEMBER
31 POSTS

Hello Joe, I got an update on my horn and cruise control issue. After replacing the Clock spring, both the horn and CC are back to normal. I may be wrong when I said the airbag unit plastic tabs were cut, for I compared my photos to a similar airbag on eBay and tabs length looks the same. My apology if I misled anyone out there. I have not yet worked on my 3rd brake light and if I do, I will update on that also.
Thanks,
Mo

Oct 1, 2021 at 5:54 AM

JACOBANDNICKOLAS

CERTIFIED EXPERT
110,175 POSTS

Hi,

Thanks for the update. I'm glad to hear you got it working. As far as the third brake light, let me know if I can help.

Take care,

Joe

Oct 1, 2021 at 9:01 PM