Brake light fuse blows when pedal NOT pressed! (pics)

Vito V6

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Hi guys please help,

If I keep brake pedal pressed & start engine all is fine but soon as let go of brake pedal the fuse blows, no brake lights & EPS + ASR light on!

The Yellow/Black wire on brake light switch is return signal telling system pedal is Not being pressed but is shorted to ground somewhere causing this issue, connector in pic below:
Screenshot_2017-03-05-17-06-24.jpg

I've cut this wire temporarily at this connector, still get EPS + ASR light once let go of brake pedal but the brake lights work fine now & fuse fine.
Question is where does this wire go or where could fault be?
I can run a new wire as would be easier and quicker than take half dash apart, I thought it was wire (no.1) in fuse box as was same colour but not it :dk:
Screenshot_2017-03-05-17-05-44.jpg

This is the fault code:
20170222_192847.jpg

It's a Vito w639 v6 120cdi 2009
I have replaced the brake light switch and disconnected the tail lights to isolate the problem, so any info much appreciated, Thanks.
 

Codger49

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Looking at a wiring diagram for an ESP equipped 639.815, the black/yellow 0.75 goes from pin 2 on the 4 pin stop lamp switch (S9/1) to pin 7 on the fuse and relay block (K40/9).
 
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Vito V6

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Hi, thanks for reply, where is this pin 7?

I have a fuse box layout diagram but not sure :confused:

Screenshot_2017-02-23-19-21-59.jpg
 

Codger49

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Don't know about the physical connection to the fuse and relay box, but pin 7 is connected to fuse f14 Brake System fuse (7.5 amp). Pin 8 which maybe near to pin 7 goes to ESP control module, if you can locate this and its leads back to the fuse and relay box it might help.

PS on the fuse and relay box diagram, there was a label 'C1' alongside pin 7.
 
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Vito V6

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Thanks again, I tried to take apart fuse box but was not to confident so left it for now, but I was able to find a few more diagrams though :thumb:

So this is the problem wire:
Screenshot_2017-03-06-19-29-06.jpg

Found this pic online, under side to the top part of fuse & relay block I believe (k40/9)? it has 9 connectors & am I right in saying I just need to find that black/yellow wire here & test if it has continuity to ground?
Mercedes-Benz-Vito-W639-Fuse-Box-A6395450401-_57.jpg

Their is another large rectangular module which connects to the 13 pins across the top & after finding this pic I see that it can be disconnected & explains why I couldn't get it out enough to see underneath properly :doh:
 

Codger49

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That is a very useful photo, its the one diagram that is either missing from WIS or I couldn't find it.

It also shows that the upper RH rectangular socket has 'C1' stamped below it. Pin 7 has got to be in there.

I did look at diagrams for the large connectors over the top, but didn't find any BK/YE wires in them. There are some other BK/YE wires around the engine, I found one is used on Parktronic.
 
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Vito V6

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Thanks, I managed to get to the k40/9, what a headache, this is the C1 connector but pin 7 has 2 pink wires with red stripes & pin 1 actually has the black/yellow wire?
20170307_120455.jpg

However this is the other large rectangular connector on left hand side:
20170307_123125.jpg
Pin 7 here appears to be the black/yellow wire from stop lamp switch, but if I unplug this connector the short to ground disappears from the wire :eek:

so seems like the problem on this wire is coming from elsewhere on the fuse block?
 
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Codger49

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There is a note in WIS about a change of K40/9 units, may be best if you post or PM me your VIN, so I can be more sure of getting to the correct diagrams.

Found an internal connection diagram for k40/9 which indicates f14 is between the k11 Circuit 15 relief relay and pin 12 in connector MK2.
On this diagram C1 pin 7 is linked to MK2 pin 9. Looks like there's more than one version of 639.815 wiring, VIN should resolve this.

PS If you include your email address, I can send you pdfs of the diagrams.
 
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Codger49

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Thanks for the VIN, now found the ESP wiring diagram which matches your photo of your connector 15 (large rectangular connector on left hand side).

The BK/YE from the brake switch (S9/1) goes to connector 7 in pin 15. It appears to be directly linked to connector MK2 pin8 which goes to pin 36 on the ESP control module with a 0.75 BK/BU lead.

Have emailed you a pdf of this diagram.
 
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Vito V6

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ah those diagrams helped, thanks, I was able to locate wire 0.75 bk/bu on MK2 pin 8, unplugged this connector & continuity to ground issue disappeared on the brake lamp switch wire, so now...

Where is the N30/4 ESP module?

Seems the issue is either the N30/4 unit or the bk/bu wire coming from it via pin 36, this wire appears to head into the passenger side cabin area from the fuse box.

Screenshot_2017-03-09-21-43-45.jpg
 

Codger49

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Have emailed a pdf of the ESP cu location.

(May be on offside as MB have a habit of only illustrating for LHD vehicles.)
 
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Vito V6

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Hi, just an update on the issue...

I tested the Black/Blue Wire on pin 36 at ESP module & can confirm it is shorted to ground, causing fuse to blow :mad:

Any ideas what to try next?
Fault codes are still; P1876 & P1906 Fault in CAN communication with N30/4 ESP

Unless the esp module itself has become faulty, could the issue be coming from another wire here :confused:
Also these codes are from a generic scanner so could be inaccurate, could MB star diagnostic be more accurate & possibly point to a sensor or other component?
 

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