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Mercedes C Class Coupe W203 2001 - Horn does not work, radio controls work in reverse - Fixed #

Posted by Kristopher Sheridan on December 12, 2014, 1:27 pm

Year of Manufacture *: 2001
( Optional ) Engine Code or CC: C180 petrol

Good Afternoon all,

we currently have in the workshop a mercedes c class with an interesting issue, the horn does not work, the radio controls work in reverse and when you opperate the horn button, the volume increases on the radio!

we have looked on E3 for diags and Alldata but none available,Put a request in to all data so just waiting to hear back from them, but does anyone have any wiring diags handy for this?

according to alldata its a Linbus system from the steering wheel buttons to steering column module then its canbus to interior and engine...

Re: Mercedes C Class Coupe w203

Posted by Anthony Pickering <iframe src='https://members4.boardhost.com/ukautotalk/info/user=ukat3715' width='330' height='300' border=0 style='border:none;'> on December 12, 2014, 1:53 pm, in reply to "Mercedes C Class Coupe w203"
Anthony Pickering

I'll check AD in a bit but is there any live data pids to confirm/deny what you are seeing? Maybe a config issue (I don't work on a lot of mercs so not 100%).

Re: Mercedes C Class Coupe w203

Posted by Kristopher Sheridan <iframe src='https://members4.boardhost.com/ukautotalk/info/user=ukat3659' width='330' height='300' border=0 style='border:none;'> on December 12, 2014, 2:38 pm, in reply to "Re: Mercedes C Class Coupe w203"
Kristopher Sheridan

Hi Anthony, Thanks for your reply, No fault codes for this and cant seem to find the relevant live data for it either.

From what i can see, the steering wheel buttons are on a LIN style network to the steering column module, and then the steering wheel control module translates this to communicate on the relevant can networks.

im sure we are meant to have at least 12v on one of the wires if it does run on a LIN style network, as surly the switches need a power supply to function and send digital messages?

Re: Mercedes C Class Coupe w203

Posted by andyhyoung <iframe src='https://members4.boardhost.com/ukautotalk/info/user=UKAT5148' width='330' height='300' border=0 style='border:none;'> on December 12, 2014, 4:00 pm, in reply to "Mercedes C Class Coupe w203"
Andrew Young

Have you tried a battery re-set?

Fixed #

Posted by Kristopher Sheridan on December 19, 2014, 9:44 am, in reply to "Re: Mercedes C Class Coupe w203"
Edited by board administrator December 22, 2014, 12:17 pm

This vehicle is fixed, Scoped the 4 wires on the switch packs on the airbag and found there was a pulsed +ve and -ve across 2 wires, earth on the 3rd and PWM on the 4th for illumination of the key pads,

When ever you opperate a button it alters the voltage threshold on the signal wires.

It appears each of the buttons run through a resistor and the vehicle must respond to the different step up or down in voltages to command the stereo/multifunction display and horn.

2 new switch packs cured this vehicle.

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