Radio controls on the multifunction steering wheel were not working, horn was working.
Fault Codes Present:
Need to determine.
Dealer worked on car, stated it was clock spring either failed (I presume open circuited) or shorted and caused control unit in the steering wheel to fail.
A8-911-Rover stated that he brought his car to the Audi dealer to have his radio controls on his 2000 A8 multifunction steering wheel looked at. After troubleshooting, the dealer stated that the clock spring (I presume F138 Airbag Spiral Spring/Return Spring with Slip Ring) failed (either open or short circuited) and caused the control unit in the steering wheel to fail.
After looking at the Bently, several things could of caused the failure. Components in the system include:
Control unit in steering wheel (E221) This is the controller for the heated steering wheel (turns it on/off), radio and phone controls by providing input to control module for multi-function steering wheel (located in relay panel under driver's footwell), horn button and airbag igniter. There needs to be sliding contact because the steering wheel rotates; therefore slip rings and spiral rings are used. I do not know the configuration, but it appears that the airbag uses two spiral springs, the horn uses two spiral springs and the radio controller uses one spiral spring. There are also two sliding contacts for power and ground to the controller.
If the radio controls were the only thing not working before bringing it to the dealer (and after looking at the wiring diagram the heated steering wheel could of or could not of worked also), it could be the controller section for radio controls OR the power supply/ground for the radio controller section. This is powered by fuse ST2 S2 (10A). To check the fuse, take the carpet out of the passenger footwell, remove the fuse box cover in the passenger footwell, then look at the second row of fuses from the top, it is a red fuse either the second one from the beginning or the end. I do not know why it would have blown, but must be checked.Control Module for Multi-Function Steering Wheel (J453) The output of the control unit in the steering wheel is the input to the control module for the multi-function steering wheel. This control module is located in the relay panel under the driver's footwell. It is located in relay position 3 & 4. This module takes input from the control unit in the steering wheel and outputs it into the radio, i.e. it interfaces the two. If this component did not work, then the heated steering wheel would work (because it only interfaces with the control unit in the steering wheel) but the radio would not work. The horn also works independently of the control module for multi-function steering wheel. If the horn worked before, there is a good chance the control unit in the steering wheel is good.
First, check fuse ST2, S2. If it is blown, maybe something happened while the dealer troubleshot the steering wheel such as touching something positive to ground causing the fuse to blow. If blown, replace it. Perform operational check of the horn, if it works, you are back where you started.
Check the fuse for the control module for Multi-Function Steering wheel, fuse ST3, S4. This fuse is a 10 A (red) fuse on the third row down on the fuse panel. Make sure it is good, if not, replace. If it is bad, you've probably fixed your problem, but there was a reason why it blew in the first place that probably needs to be fixed.
Fuse Panel on Right
If it still doesn't work, you will need to pull fault codes for both the steering wheel control unit and control module for the multi-function steering wheel. There are only two fault codes for the steering wheel control unit. If the control is bad, you do need to replace the entire steering wheel. Or it can have open circuits that need to be repaired, the springs/sliding connections would be a good place to look at. Once again, never seen it, so I am not familiar with its configuration.
First, check the two fuses, see if you can get fault codes from the dealer (or buy the ross-tech software yourself) and report back.
If only the radio controls didn't work before, but horn did, if you could determine if heated steering wheel did or did not work (ambient temperature must be less than 70F inside car, turn on driver's heated seat) that would really help in determining which module is bad.
However, if the horn use to work and now it doesn't after bringing it to the dealer, they definitely did something to screw it up, hopefully fuse ST2 S2 is blown because they touched something to ground, which will cause the horn to no longer work.