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2001 SLK230K
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Discussion Starter · #1 ·
Gas Font Motor vehicle Audio equipment Machine

Circuit component Hardware programmer Electronic engineering Gadget Electronic component

Circuit component Hardware programmer Passive circuit component Gadget Electronic engineering

Hi all,

Hope I don't get in trouble for starting a new thread - the big K40 Relay thread seems to be closed for new replies.

My 2001 SLK230 has always run fantastically, annual services, no bother. Last week I drove 200 miles north from London and when I got back, after turning off the engine and getting out the car, I noticed the fan was still running. I thought it'd go off eventually, and it did - but only because it had drained the battery.

I couldn't recharge the battery so I had to get a new one, but as soon as I connect it the fan starts up again. I can start the engine, drive it fine, but the fan just runs on at high speed unless I disconnect the battery.

I've seen lot of people with the problem, but for the life of me I can't see any specific solution except one - replacing or re-soldering the K40 relay. I've taken the K40 out and had a look, but before buying one off ebay thought I'd try re-soldering. Thing is, it doesn't actually look (to me) like it needs one. I have never soldered a thing in my life so I might be blind to the damage, but those pins in the top right look fine to me - certainly not like the examples of burnt out / damaged pins I've seen on here.

Can somebody take a look at the images and let me know whether this does actually look like it needs soldering? I might try anyway, but given the age of the thing I can't really afford to throw away the money on a replacement unless there's at least a very good chance that this is what's causing the problem.

Thank you all,
 

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Discussion Starter · #4 ·
I can see cracking around some of the terminals. What have you got to lose by re-soldering?
I've never soldered before, so I just wanted to be sure that it was an avenue worth exploring before I do. If you think it is then I'll watch some videos and get a solder kit from Amazon.

Thanks for your quick help - really appreciate it. Any practical tips for the solder?
 

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2001 SLK230K
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Discussion Starter · #5 ·
Yup, several cracked joints. Re-flowing may cure the issue......
If a component has failed then a new K40 from MB is the best solution. Too many poorly manufactured copies about.
Yeah I've seen some on eBay but not sure if they're a good idea - seem to fluctuate quite wildly in price...
 

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As you already have been pointed this:
Automotive lighting Automotive tire Gas Automotive exterior Bumper

Is not good. The surface should be smooth as teardrop, let's say.
I have advised people to visit Mobile Phone repair shops, as they are on each corner, but the TV repair man can do it too.
If not too much too ask can you upload a pic with the part number of your K-40 theat is printed on the plastic box. Just curious nothing else.
 

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Indeed :confused:
Thinking aloud .. it seems odd that there are no other symptoms that are associated with K40 failures .. atm it's just the cooling fan .. which has its own controller ..
Might be piece of the puzzle, might be nothing...anyway the controller of that fan needs power supply too. I am not in search mood, to dig into the wirings and figure out is it (indirectly) coming from the k40 or ...need beer, food and shower. Probably more beer...
 

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2001 SLK200K/2001 SLK320
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Might be piece of the puzzle, might be nothing...anyway the controller of that fan needs power supply too. I am not in search mood, to dig into the wirings and figure out is it (indirectly) coming from the k40 or ...need beer, food and shower. Probably more beer...
There you go ..
Rectangle Slope Font Parallel Pattern


Further testing required but atm I'm not convinced that it is the K40 :unsure:
 

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There you go ..
View attachment 621360

Further testing required but atm I'm not convinced that it is the K40 :unsure:
Looks like you are correct!
Hot all time, sounds like non stop, so ...there is a potentially busted fuse (resistor, capacitor......) inside the controller that is sending 100% rpms right NOW signal...
 

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2001 SLK200K/2001 SLK320
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Looks like you are correct!
Hot all time, sounds like non stop, so ...there is a potentially busted fuse (resistor, capacitor......) inside the controller that is sending 100% rpms right NOW signal...
Yes, the fact that the fan runs with Ign. OFF (always thought that was more of a secondary K40 symptom rather than a primary w/Ign. ON unless I'm missing something?) and the car is showing no other dodgy K40 symptoms, does kinda lead away from the K40 even though that particular one does look a bit suspect in one or two places :unsure: 🤷‍♂️
 

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As Original Poster (OP) is new to us:

Marcus & Bad are on our experts list. Well worth listening too.


Couple of links that may help

Although 320



 

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Discussion Starter · #17 ·
Thanks for all the comments - I really appreciate it

I actually put the relay back in cause I was kinda hoping that just taking it out and putting it back would magically change something - it didn't. But I'll take it back out tomorrow and take a picture of the part number.

I've contacted a local smart phone repair place and sent them the photos. They're a bit unsure, but if they'll do it I'll take it. If not, I've got a soldering iron on the way from Amazon so I'll give it a blast myself.

I'll happily take a video and put it up here for you to check out. At the moment I can just reiterate that the fan starts literally as soon as I connect the negative clamp to the battery. It's very cold and wet in Nottingham at the moment, so no reason for it to be thinking it's hot. I did put the engine on and my obd scanner told me the engine was 76 which is fine, right? But anyway, the fan's coming on even if the engine is off, so that shouldn't be it.

The only other info that might help the mystery is that when I drove back from London on Monday, the car had been left in a Heathrow car park for 16 days. I got a meet and greet service and when they brought it to me when I returned, they told me that the battery had gone flat and they'd recharged it. The radio didn't function anymore but I didn't really think anything more about it. The drive back was about 3 hours, and the rain was really really heavy all the way. When it's like that I need to have the windows open and the hot air blower on full blast to clear the windscreen (got no a/c on this model). So the blower was on all the way back.

When I got back home and turned the engine off, I noticed the fan running on but I checked online and some people seemed to think it's was a fairly common event that should stop after 10 mins or so. Mine went on for an hour. I thought it had sorted itself out but realised the next day when I tried to start it that it had drained the battery. I'm kind of lodged in a small driveway so didn't have an easy way of jump starting the battery. I've got one of those portable battery boosters but the clamps are so so rubbish that I couldn't get a good connection. On the couple of occasions I could, the fan started immediately and the clamps disconnected before I could make it round to turn the key.

So I got a new battery on Sunday. Bigger, as it happens. I connected it and as I say, the fan just starts immediately. This is a week later, and the weather has been awful. When I looked around the fan I noticed that a decent amount of water had pooled on the tray beneath the engine and hadn't drained. I thought maybe the pool of water had something to do with the fan coming on, but I drained it at using a sponge and it made no difference. I was actually going to ask on here and the wisdom of drilling some drainage holes in the tray....

Anyway, I kept looking for potential solutions and I came across this k40 relay idea. I took it out and to me it looks in really good condition ( the full unit, if not the specific soldered pins).

So that brings us up to date and is everything I can think of. I'll happily try anything else you might suggest, but I'm in a race against the jaw cause the MOT is due on December 4th!
 

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At times, and depending how it was done, jump starting can be the cause of issues.
Has to be done a certain way and best avoided if possible.

Some 170 Jump/Booster start threads

This info might well add weight to the fuse implied by others.
 

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2014 SLK250
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if there is a very hot hair dryer in the house and some aluminium foil
create a funneled heat output and briefly reflow the solder … it will look like an ice cream cone … several foil layers thick … large end just big enough to be taped to the cool section of the dryer … them cut the small end to create a small 5~6mm port

tho make all good attempts to focus only at the solder

you can practice depth of focus on scrap wood … just dont set the house on fire
need about 200c and just briefly to get that nice shiny chrome dome

all this presuming your k40 thingie is the culprit
but this is quick enough of a fix so …
hope all goes well

pretend you never read this if you wanna brave it with an iron

… and dont mind me … hic!
 
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