MFSW and horn stopped working. AlteaXL 2.0 TDI 2008

[SIMC]

Hi

I have a Seat AlteaXL 2.0 TDI 2008 with MFSW.
4 buttons on each side for radio control.

Suddenly the buttons and horn stopped working. No light in buttons, no reaction when pressing the buttons and no horn.

VCDS gives me this:

Address 16: Steering wheel Labels: 1K0-953-549-MY8.lbl
Part No SW: 1K0 953 549 AQ HW: 1K0 953 549 AQ
Component: J0527 636 0070
Coding: 0002042
Shop #: WSC 04941 785 00200
VCID: 01024FE7589F1E306C-8054

1 Fault Found:
01426 - Controls in Steering Wheel (E221)
004 - No Signal/Communication


I removed airbag and inspected the buttons, but the only thing I got was the part no on the buttons (5P0 959 537)
Anyone knows this failure? Is it the buttons (5P0 959 537) or Steering wheel electronic module (1K0 953 549 AQ) that has failed? Or something else?

Please advice.

[Flash2]

Welcome to the forum.

Your fault might be caused by a break in the clockspring / slip ring behind the steering wheel. The control unit for MFSW (built into the wheel) & the horn share wiring through the clockspring.

Jim.

[SIMC]

I tried an ohm tester, and tested the slip ring. All 8 wires map trough, no short and no breaks.
I have also tried to connect the buttons (5P0 959 537) directly to the Steering wheel electronic module (1K0 953 549 AQ), without the slip ring. And that didn't bring any life to the buttons :-(

Is there any way to test the 2 modules? Or is it just to replace one part at a time until it works? Sound really expensive unless I make it the first time....

[Flash2]

Sorry I've not got back to you sooner. Are you any further forward with your steering wheel controls?

I was thinking that since the buttons aren't lighting up, perhaps the supply or ground is missing from the button control unit. Have you checked that?
Check for voltage across pins 1 & 2 of the five pin connector on the button control unit on the steering wheel. The ground is on Pin 1 (blue wire) & the supply is on Pin 2 (brown wire).

Jim.

[SIMC]

Hi. Thanks for your reply

I have just testet voltage of pin 1 and 2 (orange and blue).
And there is 11.61v when buttons are NOT connected
And 0.48v when the buttons are connected.

I my case I have the following colours:
1 Orange (I guess this is Ground)
2 Brown (LIN) What is LIN?
3 Blue (I guess this is supply)
4 Grey (Horn)

On the drawing, the buttons are "A27mf" and the Steering wheel electronic module is "A23"
IMG_1821.jpg

[Flash2]

If you have 12V (OK, 11.61V) when the button controller is disconnected and only 0.5V when it's connected that suggests there is a high resistance on either the power supply or the ground to the button controller (A27mf).

Next, you will want to carry out a couple of voltage drop tests to identify where the resistance is :

connect your black voltmeter lead to the vehicle body (ground) and the red lead to the orange wire at the controller. With A27mf connected, the voltage should be less than 0.5V. If it's higher, the resistance is on the ground side of the circuit.
If the voltage in that test is correct, then connect the red meter lead to a known good 12V supply (maybe an unused fuse connection on the fusebox) and the black lead to the blue wire at the controller. Again, the voltage should be less than 0.5V. If it's higher than that, the resistance is in the controller supply wiring.

LIN is a data bus wire.

Jim.

[SIMC]

OK.

From Ground to Orange with button controller NOT connected 0,06v
From Ground to Orange with button controller connected 0,5v

From +12v to blue with button controller NOT connected 0,06v
From +12v to blue with button controller connected 10,65v

Surely there is something wrong :-)
I got the same results then I testet from connector on A27mf and the terminals on A23, so I would assume that the slip ring is OK.

My guess is that the button controller (A27mf) has shorted, or some voltage/current chip on the output side of A23 is faulty.

/Simon

[Flash2]

From +12v to blue with button controller NOT connected 0,06v
From +12v to blue with button controller connected 10,65v

Surely there is something wrong :-)

Yeah, there is something wrong. You've got a high resistance somewhere on the power supply to the button controller (A27mf).
The voltage reading is correct when the controller is unplugged because there isn't any current flowing in the circuit. You don't get any voltage drop across a resistance until there's current flowing through it. (that Ohm's law comes in handy sometimes )

If your meter has a current setting, you can use your meter to bypass the resistance and confirm that the controller itself is OK:
Plug your red meter lead into the Amps socket on your meter then connect it's probe to the +12V supply you used in the last test.
Now touch the black meter probe to the blue wire on the controller. See if the button back lights come on with the ammeter connected. You could also try adjusting the radio volume to see if the buttons actually work.

Now that you've confirmed what the fault is, you still need to figure out where it is. So you need to move your red meter lead back to the volts/ohms socket and connect the red probe into the back of the blue/grey wire at the slip ring connector. Connect the black probe to the blue wire on the controller. With both connectors plugged in, see if your voltage is high. If it is, then the resistance is in the blue/grey wire (surly it couldn't be that easy).

If the voltage in that test is low, leave your black probe on the blue wire at the controller but move your red probe to 20P pin 17 which is the ignition supply to A23. If your voltage is high now then the resistance is internal within A23 (assuming the slip ring is good).

Let us know what you find.

Jim.

[SIMC]

I have tested the following.

Ground from A23
Supply from A23
Current 0,46A

Ground from A23
Supply from fusebox
Current 5,62A !!! (yes, five point six two)

Now i know for good that the button controller has shorted.
I will order a new/used button controller A27mf (5P0 959 537) ASAP. I just have to find one first :-)

Thanks for your help. I really appreciate it.

/Simon

[Flash2]

Hello again, Simon.

Yes, 5.6 Amps sounds like a lot of current for that little controller to draw.

Thanks for letting me know about your current draw test because it highlights a potential flaw on my test method, the volts drop testing. I'll have to file that away for the next time I come across a similar issue.

I think the reason for the volts drop test showing a high resistance on the supply to the button controller is the steering control unit (A23) has seen the short and switched off power to the button controller.
A kind of electronic fuse if you like. When the controller is unplugged, A23 sees the short has gone and switches the power back on, so you get voltage when the button controller is unplugged.

It's similar to what happens when you have a bulb failure. If there is a fault on one of your exterior lighting circuits on a VW (like a bulb blows), the power supply control unit switches off power on the affected circuit.

Let me know if the new controller fixes it.

Jim.