Horn and blower won't work - Mercedes Benz SLK Forum

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#1 Old 01-12-2017
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Horn and blower won't work

This is my first post (other than intro jb edit ) . Previously I had joined the club to discover how to route wiring from the cockpit into the engine area. I found that information without having to post.
This is different and I would appreciate your help. I have had an annoying rattle from behind the dash. It is "plasticy" in its sound and is very noticeable when going over a bumpy surface. I completely removed the whole interior, including the upper dash. I found everything was tight and there was no obvious source for the rattle. I incorporated extra sound-deadening and re-built the interior. The clatter was still there, and maybe even more so!
More upsetting, though, was that the horn was non-functional and the blower didn't work. I'm very thorough in what I do and even checking everything over, again, I still can't get anything to work? I have checked all the fuses in the main engine fuse-box and they're all O.K. I did take the steering-wheel off as part of the original strip-down and I haven't checked those connections, yet. I wonder if you can help, here with how to sort this out?
Regarding the rattle, I am considering taking everthing out, again and driving the car with the central consul removed. I might find the source of the rattle, that way? I then thought to inject expanding foam into the offending area to cure the rattle.? The car has been off-the-road since October 2016 and I'd dearly like to be using it again!
Please help me

David
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#2 Old 01-12-2017
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I would be very hesitant about using that foam anywhere other than filling air gaps around the door frame in my house . That stuff expands soooo much if you spray a bit too much and get it anywhere that is in the least flexible, well it'll be ballooning outwards before you can say "holy moly".

I would get some hi-density foam (like in sofa cushions), take your dash apart and stuff that stuff in there if you can't find that loose screw.

Stay away from the foam (even if they make a "low expansion" version which I think they might).

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#3 Old 01-12-2017
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Two thoughts. I have an 03 so it might be different. I have 3 different fuse boxes. One on each side of the engine and one on the left side of the dash. Another thing to check would be the k40 relay. Really common bad soldering problems in 97 through 2000. It's apparently pretty easy to repair if you know how to solder.

Hope this helps.
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#4 Old 01-12-2017
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Hi @DAJ 190

I've attached a PDF with the horn wiring in. There are some diagnostics on the sheet that may help pin point the fault.

Good luck
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File Type: pdf Horn Wiring.pdf (631.8 KB, 26 views)
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#5 Old 01-12-2017
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Quote:
Originally Posted by DAJ 190 View Post
I have had an annoying rattle from behind the dash. It is "plasticy" in its sound and is very noticeable when going over a bumpy surface. I completely removed the whole interior, including the upper dash. I found everything was tight and there was no obvious source for the rattle.
Might it be something in the air vents? In my old BMW I had a similar sounding rattle. I found that the previous owner had had children in the car and they'd posted a small piece of Lego in through the air vents. Boy was it a relief when I found it!

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Originally Posted by Mn car guy View Post
Two thoughts. I have an 03 so it might be different. I have 3 different fuse boxes. One on each side of the engine and one on the left side of the dash. Another thing to check would be the k40 relay. Really common bad soldering problems in 97 through 2000. It's apparently pretty easy to repair if you know how to solder.

Hope this helps.
Be warned. My 2002 K40 from a facelift R170 has had the same issue you mention so poor soldering may affect a wider range than just upto 2000!!
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#6 Old 01-13-2017
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Thanks for your help, Guys! So often, when work is done something just happens to stop working, completely coincidentally, but not as a result of that work. I see that the relay, K40, serves both the horn and blower circuits? So it may well be the culprit? I'd imagine that it is a very expensive item purchased new from a Dealership? I could do with trying another K40 relay first, to see if that is the cause .... from a Breaker, or has anyone got a spare for me to try? It is a simple "in-out" operation to test it? The rattle is irritating, to say the least! Especially when nothing was found to be loose, when I had completely stripped the dash out! There just didn't seem to be anything to actually rattle! Maybe it's internal, inside the fan or the instrument cluster? I can attempt to drive the car with as much of the dash removed as is possible. It might then be obvious where it's originating from? So, has any member got a spare K40 relay that they could let me have, either to try or to purchase? Thanks

David
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#7 Old 01-13-2017
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Re solder first. Free, and is probably the issue.
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#8 Old 01-13-2017
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O.K., but where is it? There is just one relay that's obvious in the front fuse-box. It has "247" in white numerals it .... is that it? I'm pretty handy with soldering, so I'll have a look at it, if that's K40 ..

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#9 Old 01-13-2017
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Quote:
Originally Posted by DAJ 190 View Post
O.K., but where is it? There is just one relay that's obvious in the front fuse-box. It has "247" in white numerals it .... is that it? I'm pretty handy with soldering, so I'll have a look at it, if that's K40 ..

David
The K40 is a complete relay control module. There's a long thread on repairing this unit here.

As to where it is in the car, have a look here for its location.

although considering the changes you made to your car prior to the fault I'd check that you've not forgotten to plug in a connector around the steering wheel?
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#10 Old 01-13-2017
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Quote:
Originally Posted by savcom View Post
The K40 is a complete relay control module. [URL="https://www.slkworld.com/slk-r170-general-discussion/1030-k40-relay-module.html"]
although considering the changes you made to your car prior to the fault I'd check that you've not forgotten to plug in a connector around the steering wheel?
Yes, that's a fair comment. That's just what I'm going to do, right now! Although it's BOTH the horn and blower that aren't working? Anyway, lets take the airbag off and have a look? I'm usually quite thorough and it would be a surprise to have missed a connection ...

David
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#11 Old 01-13-2017
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Quote:
Originally Posted by savcom View Post
The K40 is a complete relay control module. There's a long thread on repairing this unit here.

As to where it is in the car, have a look here for its location.

although considering the changes you made to your car prior to the fault I'd check that you've not forgotten to plug in a connector around the steering wheel?
I first read about this when I had a Chrysler Crossfire (Essentially a hardtop R170 SLK320) 1˝ years ago. It was a 2004 with only 5,600 miles. I read about that K40 issue and checked mine and while I had no issues, the solder joints were not as bad as some pictured, they were not great. Years ago I worked quality control at a Rockwell plant inspecting solder joints, and they were definitely not good. I re-soldered them to prevent any issues. Mainly on the pads where the main harness connects to the board. I have read of the relays also needing replaced over time.
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#12 Old 01-13-2017
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O.K., there's not much to miss under the airbag! Yellow wire to the tag on the LHS and grey wire to the tag on the RHS. Airbag plug in the centre. All are fine. So unless there's a wire/plug near the instrument cluster, i can only assume that it might be the K40 relay? Strange, though, that only the blower and the horn are affected? I might start to take the dash apart again, to look for the rattle and I can look for any plugs/wires that are not connected, but I doubt that ... I'll have a look at the relay next and take it from there.

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#13 Old 01-14-2017
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The K40 relay is in pristine condition. There is no evident of burning or defective solder joints. All fuses are intact.It's truely mint! So what could be stopping the blower and horn from working? Previously, when routing a wire through the main fuse-box, I had detached a series of earth points, but they can only go back on the correct pin position, because they are of different diameters. Anyway, there were a couple of occasions when the car wouldn't start. I cleaned the battery terminals and it didn't happen again (and I know that the blower worked, too) Any ideas as to what to look at next? I could start to take the dash apart, but it is quite a bit of hassle! ( I could find where the rattle is by doing that) Thanks

David
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#14 Old 01-14-2017
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Quote:
Originally Posted by DAJ 190 View Post
The K40 relay is in pristine condition. There is no evident of burning or defective solder joints. All fuses are intact.It's truely mint! So what could be stopping the blower and horn from working? Previously, when routing a wire through the main fuse-box, I had detached a series of earth points, but they can only go back on the correct pin position, because they are of different diameters. Anyway, there were a couple of occasions when the car wouldn't start. I cleaned the battery terminals and it didn't happen again (and I know that the blower worked, too) Any ideas as to what to look at next? I could start to take the dash apart, but it is quite a bit of hassle! ( I could find where the rattle is by doing that) Thanks

David
If you are good at soldering re-solder the power inputs anyway. Did you look at them with magnification?
This was from my 2004 with less than 10,000 miles on it. You can see the ones on the left do not have good contact. The last picture is after re-soldering with good flow and wicking. (the brown is just the flux)
Also, you can test the circuit while the board is out and still connected I believe, jumper or check the appropriate relay points for voltage when someone tries the horn.
Attached Images
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File Type: jpg 2.jpg (23.4 KB, 1 views)
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#15 Old 01-14-2017
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Quote:
Originally Posted by DAJ 190 View Post
The K40 relay is in pristine condition. There is no evident of burning or defective solder joints. All fuses are intact.It's truely mint! So what could be stopping the blower and horn from working? Previously, when routing a wire through the main fuse-box, I had detached a series of earth points, but they can only go back on the correct pin position, because they are of different diameters. Anyway, there were a couple of occasions when the car wouldn't start. I cleaned the battery terminals and it didn't happen again (and I know that the blower worked, too) Any ideas as to what to look at next? I could start to take the dash apart, but it is quite a bit of hassle! ( I could find where the rattle is by doing that) Thanks

David
Did you look at that PDF I attached David? There are some diagnostics there that may help you work out what's wrong. All you need is a simple voltmeter to carry them out.

I'll look up the blower circuitry too and see if I can get a similar diagram for that too.
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Did you look at that PDF I attached David?
Yes I did and thanked you for your help .... it's much appreciated! I'm already finding this Forum helpful and friendly!

Now I've looked at the K40 relay using a 10X mag. eyepiece. Sure enough, the soldered pins for the power input do look "dry". There isn't that smooth solder "flow" around certain pins. No burning, though. So I'm going to re-solder any suspect pins. I'm wondering if there are any Members quite near to me? Is there a way to find that out?

David
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#17 Old 01-14-2017
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Originally Posted by DAJ 190 View Post
Yes I did and thanked you for your help .... it's much appreciated! I'm already finding this Forum helpful and friendly!

Now I've looked at the K40 relay using a 10X mag. eyepiece. Sure enough, the soldered pins for the power input do look "dry". There isn't that smooth solder "flow" around certain pins. No burning, though. So I'm going to re-solder any suspect pins. I'm wondering if there are any Members quite near to me? Is there a way to find that out?

David
I may be teaching you to suck eggs here, but all I would add is to make sure you have a good, powerful soldering iron. A small 15W electronics-type iron won't get enough heat into the joint to solder it properly. If you can, use a 30W or better iron and good solder. Keep the bit clean and wet with solder and feed new solder to the joint when it's good and melted.

Meanwhile I'll look up the blower circuitry.
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#19 Old 01-14-2017
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I use an "Irodo" solderpro 120 gas soldering iron which has variable heat. I have resoldered the pins on the K40 relay. The horn and blower are still inoperative. When refitting the centre consul, there was a 10-pin spare plug that was still unconnected. It had only two earth wires to it and I could see that it was almost certainly a redundant plug that was used to connect the originally fitted radio. That was a Mercedes unit and the plug matched socket position 3, the CD connection point. I just cannot recall any connections that I may have missed when I reassembled the dash? I did not remove the instrument binnacle but I did remove the front face from it. I think that I may now remove the lower sections from the drivers side of the dash and maybe the binnacle front cover? I can't recall any wiring there, though. I will refit the steering wheel and with dash components still removed, I'll drive the car over uneven road surfaces and try to locate where the rattling noise originates from? I'll still have this horn/blower problem, though. I'd so like to be using my SLK again, that's for sure! Would it be worth trying another K40 relay, anyway? That's why I asked if another member might have a spare that I could try?

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FWIW, I too had an annoying rattle in my Magnum "dash area" but god knows where it was in reality. There were no "loose parts" rattling around, it was the dash itself vibrating.

When I had to get the windshield replaced, I had them stuff stiff-cell foam padding under the dash as there was really easy access with the windshield out of the way.

There is a gap between the dash and the windshield (surprisingly large when the glass is removed). Trying to shove the foam in between the glass and the dash proved difficult as you can't really judge how much to put in there (and where).

I know it's not a viable solution for you (ie removing the windshield) but if you can remove the dash, find some upholstery (or firm) foam to make a new "bed" for the dash to rest on.

Worked for me.
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