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Registered 2004 SLK200K
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7 Posts
Hi guys,

I am having the intermident starting issue...
No crank at all and the fan is working full speed. The battery is fully charged. It has done it on me 3 times the last 3 days.
So I removed the k40 relay to check it but I couldn't find any issues...
No burned solders or anything like that. Have I missed something reading through the topic? What should I check next?

Regards!
 

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Administrator 2009 SLK 55 AMG/Founding member 2006
Joined
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94,192 Posts
this sounds very familiar....didn't i get that part number for someone recently?
 

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Administrator 2009 SLK 55 AMG/Founding member 2006
Joined
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94,192 Posts
Could someone please tell me if this is the correct p/n for my car? 170-545-02-05

VIN: WDB17044427306137
that vin has too many digits
17 only
 

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Administrator 2009 SLK 55 AMG/Founding member 2006
Joined
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94,192 Posts
A 170 545 02 05
relay
engine management
 

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Administrator 2009 SLK 55 AMG/Founding member 2006
Joined
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94,192 Posts

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Registered 2004 SLK200K
Joined
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7 Posts
This is the vin that I found on my V5. I will compare it with the one on the car.

Thank you for the reply. Sadly I cannot find any online stores selling it in England.

I guess the only way is the Mercedes dealership.

If you know any electrician that could check it around Birmingham let me know please.
 

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Administrator 2009 SLK 55 AMG/Founding member 2006
Joined
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94,192 Posts
This is the vin that I found on my V5. I will compare it with the one on the car.

Thank you for the reply. Sadly I cannot find any online stores selling it in England.

I guess the only way is the Mercedes dealership.

If you know any electrician that could check it around Birmingham let me know please.
you have too many digits...is there a space after the first 17?
 

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Registered 1999 SLK230
Joined
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2 Posts
I had the problem of '99 230 slk engine randomly cutting out at about 100kmh, was dangerous as this happened twice on the motorway. removed K40 relay, cleaned and re-soldered the 3 top left points, car now has quicker acceleration, more power and never cut out again :)
 

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Registered
Joined
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2 Posts
Hello guys, thanks for this post et sorry for my bad english (I am french).

I had the same weld problem in the electrical seat relay of my 320 (impossible to move the seat). I repair it and then, I reinforced the welds on my K40 because they're the same causes !
 

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Registered
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9 Posts
Mine had an external relay when I bought the car.
The wire for the relay was twisted onto braid of third relay and would cut motor when it was moved.
I left external relay and just did correct solder with plugs until spring to assess the issue.
No traces were burned at all.
 

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Registered
Joined
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9 Posts
Does anyone have a list of what the fuses control on the k40 and the others under the cover.
I cannot find it even in the wiring diagrams I bought recently.
 

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Premium Member 2001 SLK200K, 2001 SLK320
Joined
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1,491 Posts
Does anyone have a list of what the fuses control on the k40 and the others under the cover.
I cannot find it even in the wiring diagrams I bought recently.
They should be the same as the Crossfire - HERE - but even the info there is wrong as fuse 3 is 20 amp yellow :unsure:
 

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Registered
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22 Posts
Hint to assist removing the stubborn connectors -> there is a small thru-hole in the top cover of each connector.
By sticking a pick tool (straight rod) through, it can really assist you wriggling the connector out.

I'm glad to say this was one of the easiest repair/maintenance jobs I've undertaken.
Thanks Bazzle and All of you.
 

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Registered 2001 SLK230
Joined
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60 Posts
My symptoms: Warm summer day, I go to the garage to start my 2001 SLK 230 (JDM / RHD). Cranks, fires up, 2 seconds later engine quits. Turn key off and on. It makes all the normal pump and other noises, but does not crank. The starter motor acts as if it has been unplugged. Made sure the battery was fully charged... BTW, a lot of postings will go overboard about the battery. Yes, make sure it is charged, the R170 needs a good battery, but it is fairly clear that the electronics on the R170 are not built to Mercedes standard and as they age, they fail. The first suspect is not the battery, it's the electronics. This is good news for bargain hunters, because the dealership quotes prices so high that the car is not deemed worth it but for those in the know, it is not a killer repair - especially if you have access to a circuit-board electrician. But I digress...

A review of various forum postings point to a weak K40 relay. In some cases the soldering has cracks. So, I removed it, popped off the plastic cover and found no cracks in soldering, but did find some of the pins were discoloured and copper windings were three different colours. See the photos below. Pelican in USA sells replacements for US$185, plus $47 shipping to New Zealand, so I put in an order. 8 days later, it arrived and took about two minutes to install. Car started instantly and normally.

Here is the new one and the old one:
571429




Normally, I do a lot of diagnostics before spending money, but in 2017 I had a nightmare of error codes, limp mode and symptoms that pointed to a bad brake system on the SLK. Finally, I found postings about bad solder joints and replacing the computer fixed it. I found a matching computer in a wrecking yard for NZ$250 and it took 15 minutes to install. All codes, symptoms went away. There was nothing wrong with the car (brakes or whatever), the monitoring system was bad.

So, it made sense that this 19-year old car would have other weaknesses in circuit boards which is why I rapidly zeroed in on the K40 relay.

Tips for remove and replace. The electronic connectors are easier to remove if you buy a "J" tool from your local electrical supply store. It looks like a small screwdriver with the end bent like a J. After removing ignition key, disconnecting battery and providing enough light to see, pop off the plastic cover (other postings tell how to find it), and insert the J tool so you can pull the connectors directly up. They do not have catches on them, just held in by friction. Then unhook the two spring clips on the end and lift the relay out. Reverse to reinstall. Remember to follow "replace battery" procedures to reprogram. Do not throw the K40 away. One day there may not be a supply, and having a unit that can be rebuilt is helpful... says someone with a 1982 G wagon that is showing its age.

If anyone has any thoughts on why the discolouration, chime in.
 

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Premium Member 2014 SLK55 AMG Silver
Joined
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1,641 Posts
Simple. Current and subsequent heating. The varnish used on copper wire tends to darken with heat. The ones going dark are probably the ones being held in permanently or for the most time and/or the drive current to the coil is a little on the high side resulting in a temperature rise and thus the discolouration.
 
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