Recently my steering wheel started squeaking while executing slow speed turns. The cause: old, hard grease on the slip ring for the horn contact. The fix: remove the wheel, clean up the old grease, apply new grease. Please note there is no airbag on my wheel. If you have an airbag you need to disconnect the car battery at least 1 minute before you start, then unplug the airbag (orange connector under the bottom cover of the steering column). The centre of the wheel also comes out differently, I think it’s held in place with torx screws from behind.
Anyway, the procedure for non-airbag wheels starts with prying out the badge from the centre of the wheel. There are small tabs that extend into the wheel plastic, at the top and bottom of the badge. When you have removed the badge you will be able to see the nut. At this stage it is best to mark the position of the wheel in relation to the steering column, I scratched a little index mark on the end of my steering column. This helps when you come to put the wheel back on.
Make sure the indicators are off, the ignition key is removed, and the steering wheel lock is on. Using either a 22mm or 21mm socket (depending on year) and extension bar, remove the wheel nut. Insert the key and turn it to position 1 and back to unlock the steering wheel, then remove it by pulling it straight off.
When I removed the wheel I found brass shavings from the ring and the contact all over the steering column.
The contact vertically above the steering column is the horn contact.
This is the inside of the steering wheel, showing the horn slip ring.
Clean off all the brass dust and apply new grease. Making sure the indicators are still in the off position, replace the steering wheel. Re-apply the steering lock by removing the key.
Tighten the nut to 80Nm. BMW say you should always use a new nut, I would agree with this. They are very cheap from the dealer. If you are replacing your wheel with a different model, you might want to temporarily re-use the old nut until you are happy with the orientation of your wheel, then replace it with a new nut.