[E34] Horn works half

[Frank87]

Situation:
Steering wheel dead center, horn works
Steering wheel left of dead center point, horn works
Steering wheel right of dead center, horn does not work, no matter how much turns

Questions:
How does the horn system work on the E34?
What can cause the above situation?

Note:
I discovered a copper brush under the steering wheel running on a circular plate behind the wheel. This does not appear to be horn related as bridging this brush did not solve the above stiuation.

[shogun]

Horn Common FAQ, Issues and Fixes
Hey guys, as you many recall, I've spent a lot of time troubleshooting my intermittent horn on my 1992 E34. Well, I finally found the issue and got it fixed! I figured since I ran through so many different checks in the horn system, I'd post what I've learned and compile a lot of horn tips in one post.

Common Issues:
1. Fuse (obvious to most, but check the fuse. should be position 9)

2. Relay (in the fusebox. usually doesn't go out, but it could)

3. Steering wheel contact points need cleaning (use contact cleaner, steel wool, fine grit sandpaper)

4. Steering wheel ground wire. Connects to the slip ring. Connections may be damaged. Repair or replace slip ring.

5. Steering wheel is not properly grounded. Trace the break in the ground. This was my issue.

6. The horns themselves are broken (rarely is this the case)

How the system works (my layman’s interpretation):
The horn works off of grounding. When you push the horn buttons (the airbag) it grounds the slipring, which gives ground to the carbon pin (that rides on the slipring surface like a record player needle) in the steering column. This ends up giving ground to the relay circuit (probably more complex then that, but you get the idea) and the horn then sounds.

In troubleshooting the horn system, it’s good to have an electrical test light, a jumper wire, and it’s really nice, but not absolutely necessary, to have a digital volt meter.

First verify that your fuse are relays are good. Replace the fuse if needed. You can check the relay by switching it out with one of the adjacent relays. If it still doesn’t work then keep searching. From there it’s a matter of finding out when and where the horn DOES work. Remove the lower steering column cover and take a jumper wire from the bare door hinge to the carbon pin (while the ignition is in the last position). If the horn sounds, then you know that portion of the circuit is fine.

If not, then you have a ground issue. Use your voltmeter set to ohms and check and see if there is resistance at the steering column shaft. Remove the appropriate panels till you see the shaft going from the steering wheel through the firewall. You will see a guibo (flex disc) at the joint in the middle of the shaft. Check to see if the lower portion is grounded. If so, check the upper portion. In my case, the ground was lost at the guibo. So I used a jumper wire from one side of the joint, over the guibo, to the other side. This gave my steering wheel ground, a my horn then worked.

If that’s all grounded properly then remove the airbag (DO A SEARCH) and clean the button contact points. Also verify that the wheel itself is grounded… it should be, as it gets its ground from the shaft. Check that the ground wire from the inside of the wheel to the slipring, is connected properly.

That should cover most of the horn issues. Basically once you know that the horn itself works, trace down the break in the ground. For me, it was that darn guibo!

Pictures: Fuse and Relay
8389
Contact Points & Ground Wire
8390
Carbon Pin
8391
Slip Ring
8392
Steering Shaft
8393
Hope this helps someone!!! written by markct335i dt. 04-01-2011

8394

It could be that your slipring is not working properly. The slipring is apart of both the airbag and the horn system. Also, your srs light might be on even though nothing in the airbag system is messed up. Once the light is on, even after you've fixed whatever caused the light to come on, it will stay on until you use the special reset tool. Messing with the airbag system, disconnecting or reconnecting the battery while the airbag is removed will trigger the srs light.

8395
common steps:
1. put multimeter on continuity test
2. touch one probe on the door hinge bolt

what i did was:
Case A:
3. touch the other probe on the lower part of the shaft (the one that disapears in the firewall... with the striped texture feel)
4. multimeter keeps silent.

then Case B:
3. touch the other probe on the higher part of shaft (green arrow) (the one going into the driving wheel)
4. multimeter beeps

then Case C:
3. turn key to accessory position (one before ignition)
3. touch the other probe on the higher part of shaft (green arrow) (the one going into the driving wheel)
4. multimeter silent
5. press horn.
6. multimeter beeps.
7. no horn sound.

Edit: I really can't see how the flex disc there, being all rubber (?) would give a ground from one side to the other... does it have metal inside? but then woudn't that defeat the purpose of the flex disc? does that dirty i have on mine be causing trouble? is it hard to remove those parts to clean?

More here, also pic of the slipring http://www.bimmerforums.com/forum/showthread.php?1630300-Horn-Common-FAQ-Issues-and-Fixes

[Frank87]

Thanks, gonna take off the airbag.

[632 Regal]

Make SURE you disconnect the battery!

Check this for pictures:

http://www.bimmernut.com/forum/showthread.php/44534-E34-530-540-power-steering-heavy?p=345342#post345342

[Frank87]

For those of you interested. I solved the problem.

There is a ground wire between the 2 steering shafts that are connected with a flex disc. Its a simple ground wire that runs across this flex disc connection. This wire was broken and by steering with the wheel, grounded on other metal parts at some point. Hence the half working horn. Ground wire renewed and all is ok now.

[Frank87]

Here's the spot without a cable.
http://img.photobucket.com/albums/v432/PMAngelEyes/Mobile%20Uploads/20160223_171055_zpstkosp7ue.jpg


Here an improvised cable. Have already fitted a better one.
http://img.photobucket.com/albums/v432/PMAngelEyes/Mobile%20Uploads/IMG-20160223-WA0015_zpsu6gdgmzt.jpg[/URL]

[Frank87]

Here's the spot without a cable.
http://img.photobucket.com/albums/v432/PMAngelEyes/Mobile%20Uploads/20160223_171055_zpstkosp7ue.jpg


Here an improvised cable. Have already fitted a better one
http://img.photobucket.com/albums/v432/PMAngelEyes/Mobile%20Uploads/IMG-20160223-WA0015_zpsu6gdgmzt.jpg

[shogun]

Great find and pics, Frank, thanks for that info. Good to know.

[genphreak]

For those of you interested. I solved the problem.

There is a ground wire between the 2 steering shafts that are connected with a flex disc. Its a simple ground wire that runs across this flex disc connection. This wire was broken and by steering with the wheel, grounded on other metal parts at some point. Hence the half working horn. Ground wire renewed and all is ok now.

Brilliant find. My horn is not working on the new car and it may well be this too, though it remains silent regardless of where the wheel is...

Thanks for the pics you followed up with too, without them I was picturing problems behind the airbag. Never seen that wire down there near the firewall. Wow!

[632 Regal]

Here's the spot without a cable.
http://img.photobucket.com/albums/v432/PMAngelEyes/Mobile%20Uploads/20160223_171055_zpstkosp7ue.jpg


Here an improvised cable. Have already fitted a better one
http://img.photobucket.com/albums/v432/PMAngelEyes/Mobile%20Uploads/IMG-20160223-WA0015_zpsu6gdgmzt.jpg

I hope you put washers between the nut and wire on the improved version.

[Frank87]

I hope you put washers between the nut and wire on the improved version.

Dont worry, did it like a pro. Similar to the pic below but with well isolated wiring:

http://www.bimmernut.com/forum/attachment.php?attachmentid=8437&stc=1