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
Contact Points & Ground Wire
Carbon Pin
Slip Ring
Steering Shaft
Hope this helps someone!!! written by markct335i dt. 04-01-2011
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.
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/sh...sues-and-Fixes