[Dave2302]

Also, well worth checking if your car has a small cooling fan it the Module Box, they are noted for causing "almost untraceable" blowing of a fuse, can't remember which one now, but at this stage it is well worth un plugging that little fan just in case
Later Cars do not have that Fan

 

[saxmanjack]

Motor 87 M1/M2 relay is a relay in the K40 (K40k9 to be exact) It's the one connected to fuse f2 that keeps blowing.

Here's the K40 diagram:
View attachment 582270

Circuit 87 connectivity is via connector A
The Z7/6 connector is from Connector E, pin 5 and there is an interconnection.

Z7/6 is part of the Circuit 87 loom. The diagram above refers to another diagram around the fuel management of the engine and it does get complicated. Hope this works:
View attachment 582271

Z7/6 connects power to:
G3/1 - downstream O2 sensor
G3/2 - upstream O2 sensor
Y58/1 - Purge control valve
Y58/4 - Activated charcoal filter shutoff valve
N48 - BAS control module

But that's not all of it. Fuse 2 on the K40 also feeds Z7/5 via relay k9 so we need to look at that circuit too:

Z7/5 connects power to:
Y2/1 - Supercharger magnetic clutch
Y32 - Air pump switchover valve
M16/7 - Recirculated air flap actuator
Y49 - Adjustable camshaft timing solenoid

So tick off what we've already tested/discounted and let's see about the rest of these.

Thanks for the info and diagrams. If the shop the isolated the fault to K40 connector E, pin 5 was correct, (black wire with white tracer), then there must be a junction box somewhere in which that wire multiplies to reach the 5 separate components it powers. Is this junction box called Z7/6? Where is it located?

 

[saxmanjack]

Also, well worth checking if your car has a small cooling fan it the Module Box, they are noted for causing "almost untraceable" blowing of a fuse, can't remember which one now, but at this stage it is well worth un plugging that little fan just in case
Later Cars do not have that Fan

I couldn’t get the damn wire unplugged from the connector. Maybe I’ll just cut it, and screw on a cap...

 

[Dave2302]

IIRC Z7/6 is a connector splice in the wiring loom around the area of the ABS Pump, but as I'm not certain, check that on Star Finder first before un taping the Loom

 

[saxmanjack]

Don’t have access to Starfinder — but I can point out the Big Dipper on a clear night!
Seriously, this is just a splice junction in a wiring harness? Thought I had bought a quality car...

 

[saxmanjack]

Wonder how many SLK owners never bought another MB...

 

[jbanks15]

I've bought 3 slks in a row since 2002

 

[savcom]

Have to say I 'used' to buy BMW. Never again. Merc all the way.

 

[Dave2302]

Thought I had bought a quality car...

You did .................

You just don't understand it, and that is not singling yourself out, far from it, it also includes many other professional garages and owners

I find MB's to be one of the easiest Cars to work on, and I have 4 ranging from 2002 to 2015, an R170 V8 SLK, S, C and E Class Cars, and I maintain them meticulously and they don't cost a fortune because I understand how they work and therefore can fix them without guessing and changing parts willy nilly

Don’t have access to Starfinder

That is part of the issue, anyone who works on MB's should have SDS, then along with all the other cool stuff on it it has Starfinder
SDS really is as essential as Spanners, Sockets and Screwdrivers

HTH

 

[Dave2302]

Have to say I 'used' to buy BMW. Never again. Merc all the way.

Agreed

BMW and even worse VAG are the work of Satan for many many reasons not just how they work, part numbering issues, incompatibility and bad design to name but a few

 

[saxmanjack]

Thanks for the words of encouragement. Never owned a BMW or Volkswagen...

 

[saxmanjack]

Shot in the dark: disconnected the small cooling fan in the module box — fuse still blows.

 

[saxmanjack]

This circuit also supposedly powers the BAS module, but I cannot find one on this car...

 

[Dave2302]

You are now at that stage where you might spend an hour tracing wiring and testing, or you might spend 3 months.

You definitely need SDS and all the software that comes with it, eg Wiring diagrams and guided testing etc etc

If it came in my shop, it would have been 2 hours for an initial diagnostic and a look see check this and that, many are fixed within that timeframe.

If not and if the owner was prepared to spend the coin it would be a case of it takes as long as it takes

Usually I have most things fixed within 4 to 8 hours. Sadly I don't have your car here

 

[saxmanjack]

Just checking in and revisiting my thread in case some fresh eyes might be aware of this problem and know of possible solution. I’ve been driving the car with the cel on and no supercharger for months now...

 

[Dave2302]

I am sorry to see that you have still not resolved your issue

The Fuse blowing issue you have means that there could be a lot of things causing your issue. This is not a common issue, but being as I work on many many cars, yes it can happen, reasons can be many and varied. As I've never had that particular issue on any of the R170's I see I can't even attempt to give you a "shopping list" of maybe's

The answers on how to proceed and find the fault are all in this thread, and also likely clues will be in the Mitchells Wiring Diagram in the DIY's ...........
My posts # 84, 89 and 94 refers to how to proceed and the equipment needed for a job like this

 

[saxmanjack]

Thanks — this just happened today:

Low coolant light came on, but expansion tank is full. Squeezed hoses, restarted car, and light still on.
???

 

[slk230red]

Also, well worth checking if your car has a small cooling fan it the Module Box, they are noted for causing "almost untraceable" blowing of a fuse, can't remember which one now, but at this stage it is well worth un plugging that little fan just in case
Later Cars do not have that Fan

For Reference:
When the #7 fuse kept blowing on my '01 SLK230, the cooling fan was the culprit. It was shorted, so I unplugged the cooling fan from the 10-3 module plug, installed a new 5 amp fuse in #7 and problem resolved.
Also replaced the cooling fan with an identical fan from a Crossfire.
The cooling fan is not listed on the fuse chart for the #7 fuse.

Also, I would like to give kudos to fellow member tl99999 (Tony) for posting his find about a defective/shorted module fan. After doing several searches, I found his post and was able to isolate my blown #7 fuse problem.

"Burnt out CCM (Roof Module)"

"Hi,

I would just like add my recent experience of this same problem to this thread. With the battery and roof module disconnected I measured the resistance of every pin on the roof module connector to chassis ground and battery positive. In my case there were no shorts to ground or battery positive. I then used the wiring diagrams to identify things that were powered completely by the roof module - motors etc and found that the module box blower motor had gone short circuit. Its only a small fan in the bottom of the module box below the roof module and has two wires to pins 50 and 67. These two pins are part of a two pin plastic housing that can be unclipped from the rest of the connector. This fan is only powered up with the ignition on and that is why pin 58 (circuit 15) burns out. Presumably Fuse 7 doesn't always blow and the module burns instead. I'm thinking of running the module box fan directly from another fused circuit so that the roof module is unaffected if it shorts out again.

Benzworld has a thread on how to replace the electric motor in the module box fan assembly.

Regards,

Tony Leach

R170 1999 SLK230K
United Kingdom"

 

[saxmanjack]

Update: took the car to another independent MB shop here (yes, he has the star system, etc, etc) .
Left it there for a few days, and he was UNABLE to find the source of the short. He suspects rodent damage somewhere, and said the next step would require taking apart the dash, because he claims the shorting wiring goes under and behind the computer board box, and that needs to be unbolted from inside the dash.

There is another guy in town who is purported to be a MB electrical guru, works out of his garage, might try him next…

 

[Dave2302]

There is another guy in town who is purported to be a MB electrical guru, works out of his garage, might try him next…

He will likely be the good guy

Quiescent current drains are very easy to narrow down if you know the correct procedures, and do not believe the muppets on You Tube etc, I have seen sooooo many videos where they are testing straight away with bonnets up / doors open etc, muppets I say, absolute muppets, ........................

All cars with Electronics, upon switch off and seeing Doors / Bonnet etc all closed then take 10 - 30 minutes to totally shut down all modules, so when tracking a drain it takes time, and the muppet should actually fool the car into thinking everything is closed, i.e. push any door pin switches in with a suitable clamp, click the locks completely closed with a small screwdriver, look for a push / pin switch on Bonnets etc etc etc, and then the testing gives meaningful results ..............

Here's one I did on a VXR Astra last week :-

Clickeable Pic ....



Conclusion being there is no current drain, muppet garage had said there was based upon the fact that yoof who owned it had fitted a new Battery, so they assumed that the Battery was good ...............

Ermm nope, after checking the Current Drains and the Charge Rate under no load and under load my conclusion was the Battery was absolutely shagged, and a Heavy Discharge Test after a full charge proved it, it dropped to under 11 Volts in around 6 seconds ...................

FWIW do not buy "Lion" Brand batteries from ECP if you're in UK, utter utter utter rubbish.