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That light is on because there has been a power interrupt (disconnected battery) - you need to reset the Steering Angle Sensor by turning the Steering Wheel ~ Left Full Lock, Right Full Lock and Return To Centre ~ light should then extinguish

Personally, I'd disconnect the fan control module and leave the K40 alone for now
 

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Discussion Starter · #22 ·
Is the fan control module the block in the bottom right I hover over in the video?
That light is on because there has been a power interrupt (disconnected battery) - you need to reset the Steering Angle Sensor by turning the Steering Wheel ~ Left Full Lock, Right Full Lock and Return To Centre ~ light should then extinguish

Personally, I'd disconnect the fan control module and leave the K40 alone for now
Is the fan control module the block in the bottom right I hover over in the video?

Will the car be safe to drive if the module's disconnected?
 

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Is the fan control module the block in the bottom right I hover over in the video?

Will the car be safe to drive if the module's disconnected?
Yes that
I've just disconnected mine by squeezing the tabs together and pulling the connector off, it took me 10 seconds but if I was planning on leaving it like that I'd probs put it in a bag or something to protect it, or go looking for the 50A fuse
Circuit component Hardware programmer Electronic component Electronic engineering Computer hardware


As I see it...
The fan won't come on, but late-November UK it won't be needed anyway - probably/maybe 🙃
The fan is designed to come on at 100c so unless you have a severe coolant loss or we get a sudden heatwave and you happen to find yourself sat in heavy traffic for an extended period it should be fine as a (very) short-term solution.

Maybe there's an issue with the controller, maybe there's an issue with the wiring, maybe there's an issue with the K40 after all but at least you won't be draining the battery every time you connect it up.
 

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Discussion Starter · #24 ·
Yes that I've just disconnected mine by squeezing the tabs together and pulling the connector off, it took me 10 seconds but if I was planning on leaving it like that I'd probs put it in a bag or something to protect it, or go looking for the 50A fuse View attachment 621373 As I see it... The fan won't come on, but late-November UK it won't be needed anyway - probably/maybe 🙃 The fan is designed to come on at 100c so unless you have a severe coolant loss or we get a sudden heatwave and you happen to find yourself sat in heavy traffic for an extended period it should be fine as a (very) short-term solution. Maybe there's an issue with the controller, maybe there's an issue with the wiring, maybe there's an issue with the K40 after all but at least you won't be draining the battery every time you connect it up.
My solder kit arrived and it came with a multimeter, so I tested the pins on the relay board and it seems to be telling me that there is good connection of those spins.... So I'll put it back and try disconnecting the fan module as you've suggested - I'll report back. btw, somebody has commented on my video to "replace the temperature sensor and clean the contacts of the fan unit" Do you think there could be anything in that? I've had the engine coolant light on my dash for a while but the local MB specialist said it was most likely just the sensor. I bought a replacement but didn't fit it because it sounded difficult (involved draining a tank, if I'm remembering correctly), and because it didn't seem to be having any negative effect at the time. Does anyone think that could be to blame?
 

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Discussion Starter · #25 ·
Ok - I've put the relay unit back and unplugged the fan module. As you say, I can now connect the battery, the engine starts fine, but obviously the fan isn't working. I plugged the module back in and it immediately starts again.

I looked again at the coolant temperature sensor replacement and I must've been looking at something else last time cause it was incredibly simple - I've replaced that sensor now. No change, but then it wasn't likely to be a sensor problem if it happens before the engine is started, right? Or am I misunderstanding how these things work?
 

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Ok - I've put the relay unit back and unplugged the fan module. As you say, I can now connect the battery, the engine starts fine, but obviously the fan isn't working. I plugged the module back in and it immediately starts again.

I looked again at the coolant temperature sensor replacement and I must've been looking at something else last time cause it was incredibly simple - I've replaced that sensor now. No change, but then it wasn't likely to be a sensor problem if it happens before the engine is started, right? Or am I misunderstanding how these things work?
Nope, you're reading that exactly the same as I am. Gotta be something amiss with either the control module or the wiring
 

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Discussion Starter · #29 ·
At least the float looks it's actually still floating in something - Yes? :unsure:
Err.. I'm not sure it was actually. I topped it up, and it took about a litre to get it looking like in your picture, floating in the coolant. I left it for a bit, and.....

the fan isn't coming on when I connect the battery! I started the engine, left it running for a bit, and when I turn it off the fan doesn't keep going. Does that make sense? Could there be a leak in the coolant tank that it's somehow detecting and running the fan to compensate?

I've unplugged the battery again for now as I didn't want it just starting up again overnight, but fingers crossed we might have stumbled on an answer or if it's totally illogical then something else might have just fell into place somehow.

I'll let you know....
 

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Well it ain't a day of waste if you learn a thing, in'it?
So the coolant T sensor you mentioned is part of the "cooling the engine" logic. So can you confirm it was all nicely clicked?
Because the high RPMS are coming as command and that command before you rotate the key to position || isn't from the engine ECU. So, it (speculation, not statement) could be the signal not being "received" by that fan control module and/or not having the expected (whatever degrees Vs open circuit) readings on the inlet results on MAX power on the outlet.
The low coolant level should have been on the DASH and if your dash works (key to | = airbags ON, key to ||= all rest of the bulbs on) the level could be low, but not scary low.
As usual, the checking of your own work repays the most. So are you sure that T sensor was well clicked?
On a side note, you do have amp meter now, remove all off the car ( usb sticks, extra phone chargers...) Close the doors, lock it. Disconnect the battery.
Set the multimeter to AMP use the 2 plugs AMP Sports equipment Camera accessory Reflex camera Audio equipment Camera
and COM,set it to max amp range and connect the negative car clamp to com and the positive probe to the battery terminal.
Readings under 0.050Amps are desirable, unde 0.025 A are a dream!
Over 0.05Amp you have problems.
Good job on identifying the issue for sure!
 

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**Premium Member '02 R170 SLK V8 5.0 & '00 SLK320
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Low coolant still won't make the fan come on when the key is in your pocket 🤷‍♂️
/\ /\ /\ This ................ Unless there has been a previous bodge somewhere to the wiring ;)

In this instance, whilst K40 does have cracked Solder, I don't think it is the issue, but obviusly it just might be, but when Fan runs flat out due to K40, on all the many that I've worked on also the Engine doesn't Start.

R170 Fan should not run on after Engine (Ignition) Off, some Cars do, R170 does not ;)

Fan runs flat out as a default setting when there is an issue. Clearly the Fan Motor is fine, so that leaves Fan Controller Module (on inner wing), or Wiring to it, or possibly a Motor ECU issue, could possibly be some weird HVAC fault too, although OP says no A/C never say never ;)
 

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**Premium Member '02 R170 SLK V8 5.0 & '00 SLK320
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Ahhhhhhhhhhhhhh ...........................

Wait a doggone cotton picking minute ............................

Now it makes sense .............................

'Dave light-bulb moment' ............................

It (absolutely, almost certainly, pretty much definitely, 99.9 % bloody surely) has to be the Fan Controller Unit itself that has shattered it's pantaloons ;)
Why ?

Because that is the only part of the equation that is fed from a permanent Battery +

Get a good used one and plug and play (y)
 
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Ahhhhhhhhhhhhhh ...........................

Wait a doggone cotton picking minute ............................

Now it makes sense .............................

'Dave light-bulb moment' ............................

It (absolutely, almost certainly, pretty much definitely, 99.9 % bloody surely) has to be the Fan Controller Unit itself that has shattered it's pantaloons ;)
Why ?

Because that is the only part of the equation that is fed from a permanent Battery +

Get a good used one and plug and play (y)
@benfrew says it's working now, or rather, it's not causing the fan to come on anymore when it's connected :unsure:
Needs a session on SDS to make sure that the fan will run as and when it's required :p


I want to know where the coolant has gone now though and maybe the clue is here in OP's intro? :-
There's also a problem where there's too much moisture in the cabin (water ingress from corrosion?), causing the windscreen to mist really quickly and thickly. In cold weather the condensation frosts on the inside of the windscreen. I don't have A/C on this model, and the hot blower only shifts it slowly and at full power, so it makes driving in winter a bit sketchy!
Usually we'd say the drains are blocked, change the cabin filter etc. ..
 

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**Premium Member '02 R170 SLK V8 5.0 & '00 SLK320
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benfrew says it's working now, or rather, it's not causing the fan to come on anymore when it's connected :unsure:
Needs a session on SDS to make sure that the fan will run as and when it's required :p


I want to know where the coolant has gone now though and maybe the clue is here in OP's intro? :-
Usually we'd say the drains are blocked, change the cabin filter etc. ..
/\ /\ /\ 100% agree, but my point is even if you drain all Coolant the Fan won't (should not) run with no Key in Ignition, it certainly didn't when I first ran my V8 with no Radiator in, nor do other MB's, That way I don't have to push them in and outta the workshop when waiting for parts.
I do that a lot if I need to move a Car without Radiator, I made up a nice little Jic fitting so I can link the Trans Cooler and avoid the 'Deepwater Horizon' effect :p
So I still say his Fan Controller is buggered ;) Perhaps coincidence that with the fan flat out all this time it has finally died for good ..................
As you rightly say Maestro II now it needs SDS to make certain it will actually work when needed (y)

Whatever yeah I agree, it probably needs a Heater Matrix, and good luck with doing that job :eek: ............

Who all remember this ....


and nope, he didn't strip it all down in 2mins 38 sec :ROFLMAO:

Still, nowhere near as bad as that 2012 Range Rover Vogue I had in 🤣
 
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Discussion Starter · #37 ·
Hi everyone,

This orning I attached the battery and again, the fan didn't come on. Amazing! I fixed the battery clamps, started the engine, and went for a drive. Everything seemed fine - the engine coolant light was gone, there were no codes on my scanner, and the car drove great. I drive it for about an hour in total, with stops, and then went to the supermarket.

I went to the supermarket, and next door there was an in-'n'-out MOT centre with a sign up saying they had slots available. So I thought, why not?!

I booked it in for later in the day, left it with them, walked home and crossed my fingers...

Unfortunately, it was too good to be true. I got a call from the centre not long ago. When they drove it in, before they even started the MOT, they'd found engine coolant had leaked out. They don't know where from. They've asked if I want them to do a diagnostic to find out where, and I've agreed, but that's another 60 quid on top of the 45 for the MOT that I'm worried might not be well used. I don't know what they'll find, but I'm not hopeful. For context, the value of the car is about 600 quid max. I could get about 320 in scrap. So even though I really want to get it through its MOT I've already stacked up about 200 quid this week and I can't really afford much more unless I know it'll get through the MOT. I'm dreading the cost just to fix the coolant leak, never mind the fan module. I haven't mentioned it here, but there is a persistent problem with the rear lights too - I've replaced individual bulbs and both full light clusters, but lights on both sides work for a bit, then stop, then work again, then stop. I took it to an MB specialist who checked the connections and ran diagnostics but they couldn't find a reason. So that was another 120 down the pan.

Anyway, just filling you all in cause you've been loads of help and I'm grateful for you all taking an interest. We'll see what happens with this coolant tomorrow....
 

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Not being funny just asking, coolant leak is or is not a MOT failure?
Knowing issue with pipe, expansion tank, etc....is not making the car "dangerous" is it?
 
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Not being funny just asking, coolant leak is or is not a MOT failure?
Knowing issue with pipe, expansion tank, etc....is not making the car "dangerous" is it?
Depends how bad it is, quote from RAC:
Coolant leak
You might be surprised to learn that leaks of fluids such as engine coolant and screen wash aren’t considered reasons for failure.
According to DVSA guidelines, a vehicle will only fail the MOT if a fluid leak creates a pool on the floor within five minutes that’s more than 75mm in diameter, or if there are many leaks which collectively leak fluid at the same rate.
 
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