Horn issues! Can't find relay!

tnics84 · November 18, 2023

Recently broke the horn in my 2018 Yukon Denali. Hit it too hard (I know, I'm an idiot). Horn got stuck on and it ended up blowing out. Took it to my mechanic (not dealership). He advised me that I needed to replace my spring coil as well as the actual horn. Fuse was fine.

After replacing both, he went to reattach the battery, and as soon as he put those cables back on the horn just starts blowing without stopping. Tried hitting the lock / unlock buttons on the remote. Tried pressing the horn on steering wheel. Nothing stops it. I've had to disconnect the horn and go without since.

Knowing that the horn, fuse and spring coil are all good, he assumed it must be the relay. Problem is neither of us have been able to find where the relay is located. I have searched the internet to no avail. What I did read on one or two forums is that the horn relay could be built into the fuse box under the hood. But nothing confirming this. I've called 3 different dealerships and spoken with parts, as well as service departments. None of them have been able to tell me. The last one I spoke with said to call GMC direct. I spoke with them and they also were unable to confirm anything.

So before I go and replace the entire fuse box, does anyone know if this is true? Is the horn relay on my truck built into the fuse box itself?

Or does anyone have any suggestions for any other diagnostics I should check before replacing the fuse box?

Very much appreciated!

-Travis

tbarn · November 18, 2023

The relay is a PCB relay (electronic). Not serviceable. New fuse block wound be required.

newdude · November 18, 2023

13 hours ago, tnics84 said:

What I did read on one or two forums is that the horn relay could be built into the fuse box under the hood. But nothing confirming this. I've called 3 different dealerships and spoken with parts, as well as service departments. None of them have been able to tell me. The last one I spoke with said to call GMC direct. I spoke with them and they also were unable to confirm anything.

So before I go and replace the entire fuse box, does anyone know if this is true? Is the horn relay on my truck built into the fuse box itself?

Or does anyone have any suggestions for any other diagnostics I should check before replacing the fuse box?

10 hours ago, tbarn said:

The relay is a PCB relay (electronic). Not serviceable. New fuse block wound be required.

Correct. Horn relay is a PCB relay internal to the underhood fuse block.

Not sure how the dealer people weren't able to find the information as its really easy to find in their service manuals but I'm sure they'd rather have tried to get you into the door for service and have the shop diag it.

Here's the list of the relays that are PCB relays serviced only with the fuse block:

Important: Relays listed below are non-serviceable Printed Circuit Board (PCB) relays and are internal to the block

KR3 Horn Relay - F93UA

KR6 Rear Window Washer Pump Relay - F115UA

KR11 Windshield Washer Pump Relay - F114UA

KR12B Windshield Wiper Relay

KR12C Windshield Wiper Speed Control Relay

M75 Windshiled Wiper Motor

KR29 A/C Compressor Clutch Relay

Q2 A/C Compressor Clutch

KR46 Front Fog Lamp Relay

F94UA (T3U)

KR48 Headlamp High Beam Relay

F95UA

KR49 Headlamp Low Beam Relay - F121UA (T4F), F122UA (T4F)

KR61 Trailer Backup Lamps Relay - F34UA, F49UA

KR63L Trailer Stop/Turn Signal Lamp Relay - Left - F40UA

KR63R Trailer Stop/Turn Signal Lamp Relay - Right - F39UA

Edited November 18, 2023 by newdude

tnics84 · Wednesday at 06:49 PM

Thank you guys for the help! And my apologies for the late reply, but wanted to follow up.

These dealerships are really something else.

I went and changed out the fuse box. This still did not work. So I finally caved and brought it in to the service department. After paying $300 in diagnostic fees, they told me they could not locate the issue and would need to just start changing out parts until the problem was gone.

At this point I was so frustrated I decided to take the horn apart myself and have a look.

Within seconds of opening it up I was able to see that one of the little metal tabs that make contact and activate the horn when you press it, was slightly bent. I used a tiny screw driver to bend it back into place and voila, problem solved