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Discussion Starter · #1 ·
Hey guys,

I have a rather unusual problem, that I have searched for not only here but another slk forum and have found a thread or two with the same symptoms but they were never finalized nor was anyone able to figure out what is causing this. So I am creating this thread so once I find the issue that is causing this I will post the answer in here clearly and yes I will find the problem hehe.

So a few months back my radiator fan quit working completely and the low coolant light turned on. Straight away I knew the issue was the Fan Control Module which I ordered brand new from AutoHausAz and replaced it.

The Radiator fan sprang back to life straight away and everything worked fine for a month or so. I just recently had MB replace a bunch of parts under warranty for the leaky cam solenoid to include a brand new ECU.

But right before I turned my car to them, I noticed my temps reaching 80c and realized that the radiator fan is not working again, at first I though no way my control module quit working again but I quickly figured out that is not the issue.

So trying a few things and like mentioned above doing some searching I have noticed that the fan does turn on weakly when the AC or heating is set to full(Defrost) like mentioned in the threads I found in the search.

I have read several threads about the notorious K40 relay and have not check it out yet as I just got the car back today, but no one in the sticky thread about has any of the symptoms I am having and I am not having any of the symptoms they are having, although I should probably look into replacing it anyways as the car has 109k miles on it already.

So I started searching and I have found a few threads with the same exact symptoms I am having but as mentioned above all the threads would just end in a dead end. Symptoms being Fan turning on weakly when full AC or Heater Defrost is turned on.

Anyways tomorrow I will check my K40 relay regardless and also provide direct power to my fan to rule out a bad fan or bearings.

Any insight would be greatly appreciated to help me diagnose this issue.

Thank you,
Mike
 

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From a search

Why an engine temperature of 80+ Celsius so high for a Mercedes Benz c230?

Most engines (speaking about automotive wide, not just within the Benz line-up) are designed to run close to that heat range.
The thermostat sets the coolant temperature where the engine begins to circulate coolant with or without antifreeze protection. Most antifreeze coolant mixed with 50 per cent distilled water will provide protection from freezing down to -40 degrees C. and up to + 125 degrees C. before boiling. Thermostats should be available from auto parts houses or an MBz dealer with temperature opening specs of 70 C. 80 C. or 90 C. In arctic weather climates, you might want to use the higher temperature thermostat. In desert hot climates you might want to use the colder thermostat. Make sure your water pump, coolant fan and radiator are working correctly without coolant loss.


so the question is which thermostat do you have?
MBz dealer with temperature opening specs of 70 C. 80 C. or 90 C

just sayin' :D
 

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Discussion Starter · #3 ·
From a search

Why an engine temperature of 80+ Celsius so high for a Mercedes Benz c230?

Most engines (speaking about automotive wide, not just within the Benz line-up) are designed to run close to that heat range.
The thermostat sets the coolant temperature where the engine begins to circulate coolant with or without antifreeze protection. Most antifreeze coolant mixed with 50 per cent distilled water will provide protection from freezing down to -40 degrees C. and up to + 125 degrees C. before boiling. Thermostats should be available from auto parts houses or an MBz dealer with temperature opening specs of 70 C. 80 C. or 90 C. In arctic weather climates, you might want to use the higher temperature thermostat. In desert hot climates you might want to use the colder thermostat. Make sure your water pump, coolant fan and radiator are working correctly without coolant loss.


so the question is which thermostat do you have?
MBz dealer with temperature opening specs of 70 C. 80 C. or 90 C

just sayin' :D

So as you mentioned in your own post to check if my radiator fan is working correctly. I am pretty well aware of temperature ranges engines work in and about MB standards.

Fact is based on my diagnostics and knowing how my coolant fan has worked before and how it should work, I know for a fact the my radiator fan is not engaging properly, also seeing how it is below freezing where I live now the car should not be getting anywhere close to the temps it is now, although still within thresholds stated by MB.

Right now my radiator fan only engages when the heater is set to defrost (full power) or the AC is turned on, and it engages so weakly I can literally stop it with my bare hands.(Please don't ask how I know. :p)

I don't want to wait till summer where it gets super crazy and humid here to try and diagnose the problem. These fans are suppose to work at three speeds and even at the lowest speed it should spin fast enough to probably somewhat butcher my fingers which is not the case at atm.

Thanks,
Mike
 

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Discussion Starter · #4 ·
Going to do a quick update.

I took my K40 out today, found one blown fuse and the top left solder was getting a little funky as per usual problems. So I went in and reflowed some solder and replaced the blown fuse, and right away I noticed a difference not only in start up of the car but also shifting and the bypass valved for the SC started working correctly, but still no go on the radiator fan issue.

I have also tested the radiator fan by giving it direct 12volts and it works nice and strong with out any noises at the bearings, and I know for a fact that my new Fan Control Module is working as well.

Anyways I understand that Mercedes specifies a little higher than normal running temps than most 4 cylinder engines. Also I am not new to the automotive world nor am I new to working on them, rebuild a few motors and even went as far as fabing up a fully functional intake manifold at one point.

As mentioned above, I understand that it's normal for these cars to hit 100c as operating temperatures, but I do not believe that when the engine does reach those temps especially at idle the radiator fan doesn't kick in at least in low mode.

I also noticed that when I turn the Heater blower knob to any range lowest or highest an doesn't matter what temps I set on the climate control the Radiator fan will turn on and turn very weakly this is with the EC turned off, the second I turn on EC the fan quits working.

At this point the issue looks to me like it might be a weak ground somewhere and the heater blower and the radiator fan share a common ground somewhere that's why it will turn on weakly when the heater blower is turned on.

Another theory I have is, I know that the Auxiliary electric water pump went bed on this car, from my research all its suppose to do is provide an extra 30 to 45 minutes of heat in the car while the engine is off.

If anyone else has any other ideas please feel free to chime in, at this point I'm not going to go out again to check for bad grounds, but tomorrow the plan is to locate as any grounds as I can, specifically on the heater blower circuitry and radiator fan, especially on or around the fan control module.

Thanks,
Mike
 

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Discussion Starter · #5 ·
Going to do a quick update.

I took my K40 out today, found one blown fuse and the top left solder was getting a little funky as per usual problems. So I went in and reflowed some solder and replaced the blown fuse, and right away I noticed a difference not only in start up of the car but also shifting and the bypass valved for the SC started working correctly, but still no go on the radiator fan issue.

I have also tested the radiator fan by giving it direct 12volts and it works nice and strong with out any noises at the bearings, and I know for a fact that my new Fan Control Module is working as well.

Anyways I understand that Mercedes specifies a little higher than normal running temps than most 4 cylinder engines. Also I am not new to the automotive world nor am I new to working on them, rebuild a few motors and even went as far as fabing up a fully functional intake manifold at one point.

As mentioned above, I understand that it's normal for these cars to hit 100c as operating temperatures, but I do not believe that when the engine does reach those temps especially at idle the radiator fan doesn't kick in at least in low mode.

I also noticed that when I turn the Heater blower knob to any range lowest or highest an doesn't matter what temps I set on the climate control the Radiator fan will turn on and turn very weakly this is with the EC turned off, the second I turn on EC the fan quits working.

At this point the issue looks to me like it might be a weak ground somewhere and the heater blower and the radiator fan share a common ground somewhere that's why it will turn on weakly when the heater blower is turned on.

Another theory I have is, I know that the Auxiliary electric water pump went bed on this car, from my research all its suppose to do is provide an extra 30 to 45 minutes of heat in the car while the engine is off.

If anyone else has any other ideas please feel free to chime in, at this point I'm not going to go out again to check for bad grounds, but tomorrow the plan is to locate as any grounds as I can, specifically on the heater blower circuitry and radiator fan, especially on or around the fan control module.

Thanks,
Mike
One more quick comment on this, I have also unhooked the Coolant Temp Sensor and as I predicted. When I started the car it threw the fan into full speed mode, this is done as a safety precaution by many car manufactures, so if your temp sensor goes bad your car wont over heat.
 

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I have the same problem. I replaced fan control module, swapped a K40 no change just like you said with EC on the fan does not turn at all. With EC off and the temp setting on blue the fan turn slow. Here's my thoughts I have a problem with my AC compressor so I always leave the EC button on to make sure the compressor is off, when the weather temp get near 70 I will get the AC compressor fixed, then I can turn off the EC button I was hoping the engine fan could run strong but now I'm not so sure. Question do you have any problem with your AC?
 

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Discussion Starter · #9 ·
For my benefit:

How do you know the fan control module is working properly?

How do you know the fan is not working properly since your temp is fine?
This is a brand new unit from AutoHaus first of all and secondly with a blown fan control module, the fan won't even turn on when the ECT sensor is unplugged nor will it turn on even weakly with the heater blower turned on.

When you unplug your ECT sensor your cooling fan should go into full speed mode as a fail safe not to over heat your motor if it goes bad while driving.

Also usually when this unit goes bad, the 'low engine coolant' light goes on.

i agree a fan turning so slow you can stop it with your hand is a "problem". Which fuse in your k40 was blown?
The second fuse was blown, I believe the fuse that was blown was for operating the SC by pass valve, since that wasn't working properly until the fixes to the K40 and replacing the fuse.

My K40 actually looks really good, except for the one spot in the top left where it's mentioned the solder can start looking bad, mine wasn't too bad but it still needed some reflowing.

Ever since I took care of the K40, the car does run a ton smoother even start ups are nice and crisp now.

I have the same problem. I replaced fan control module, swapped a K40 no change just like you said with EC on the fan does not turn at all. With EC off and the temp setting on blue the fan turn slow. Here's my thoughts I have a problem with my AC compressor so I always leave the EC button on to make sure the compressor is off, when the weather temp get near 70 I will get the AC compressor fixed, then I can turn off the EC button I was hoping the engine fan could run strong but now I'm not so sure. Question do you have any problem with your AC?
I don't have a problem with my AC, but I do know that the Auxiliary electrical water pump located in the front right fender is bad, I know that because I heard it die hehe. I need to get a hold of wiring schematics for this car to check if that's in someway connected to the cooling fan circuitry.

I know sometimes the ECT sensor it self can cause the radiator fans not to work properly, the OHM's on mine seem normal and the coolant temp gauge seems to be pretty accurate, but for a $19.00 dollar parts I can replace it, especially since this one has over 100k on it,


Like I mentioned above, I fully understand that these MB motors are made to run at higher temps, but lets be honest when my car reaches 110c at idle standing still, the radiator fan should turn on at least in low mode.

Also sorry for a somewhat late response, just started a new job and all. :)

Thanks,
Mike
 

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This is a brand new unit from AutoHaus first of all and secondly with a blown fan control module, the fan won't even turn on when the ECT sensor is unplugged nor will it turn on even weakly with the heater blower turned on.

When you unplug your ECT sensor your cooling fan should go into full speed mode as a fail safe not to over heat your motor if it goes bad while driving.

Also usually when this unit goes bad, the 'low engine coolant' light goes on.



The second fuse was blown, I believe the fuse that was blown was for operating the SC by pass valve, since that wasn't working properly until the fixes to the K40 and replacing the fuse.

My K40 actually looks really good, except for the one spot in the top left where it's mentioned the solder can start looking bad, mine wasn't too bad but it still needed some reflowing.

Ever since I took care of the K40, the car does run a ton smoother even start ups are nice and crisp now.



I don't have a problem with my AC, but I do know that the Auxiliary electrical water pump located in the front right fender is bad, I know that because I heard it die hehe. I need to get a hold of wiring schematics for this car to check if that's in someway connected to the cooling fan circuitry.

I know sometimes the ECT sensor it self can cause the radiator fans not to work properly, the OHM's on mine seem normal and the coolant temp gauge seems to be pretty accurate, but for a $19.00 dollar parts I can replace it, especially since this one has over 100k on it,


Like I mentioned above, I fully understand that these MB motors are made to run at higher temps, but lets be honest when my car reaches 110c at idle standing still, the radiator fan should turn on at least in low mode.

Also sorry for a somewhat late response, just started a new job and all. :)

Thanks,
Mike
Evening Mike, having read all of the above you have proved that the temperature sensor is not working, "unplug the sensor the fan runs" when plugged in temp gets to 110c fan does not start, looks like the sensor has failed, but failed closed, circuit made, no fan.

Just my thoughts on it.

Regards Stuart.
 

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Discussion Starter · #11 ·
Evening Mike, having read all of the above you have proved that the temperature sensor is not working, "unplug the sensor the fan runs" when plugged in temp gets to 110c fan does not start, looks like the sensor has failed, but failed closed, circuit made, no fan.

Just my thoughts on it.

Regards Stuart.
Hi Stuart,

Thanks for your reply on this matter, I would have to agree with you, because even though my temp gauge in the car seems to be working correctly, I do think the ECT sensor has failed in closed mode. I will have a new sensor available for me in about three hours, and since it is only a 10 minute job to replace it, I will get it replaced right away and report with results.

Regards,
Mike
 

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Discussion Starter · #13 ·
Hey guys,

Quick update, Been quite busy with my new job but I like it, gotta make money to fix this damn car properly hehe.

Anyways I put in the new ECT and still the same results with the fan, except this time my temp gauge seems to stay a little lower, haven't gotten passed 80c. I'm sure the old ECT was probably not as accurate anyways which would explain my out of spec OHM measurements.

I was wondering if someone could do me a huge favor, if you could have your car reach to what you think are operating temperatures and check if your Radiator Fan actually kicks in at any given time. It's still somewhat cold where I live so the temps even at idle have a hard time reaching 80c at this point, we're suppose to get some nice warm weather here during the weekend so I can do more testing, but I am curious as to what I hear from others.

I am still trying to track down a decent wiring schematic for this car, to see if the AUX Water pump that went bad on my car is in any point included in the circuity of the cooling system, which also might explain my current issues.

Thanks in advance,
Mike
 

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Discussion Starter · #15 ·
Awesome thanks for this actually.

So it seems like the AUX water pump which they call the coolant circulation pump and the engine/climate control electric cooling fan(radiator Fan hehe), are on two different circuits and have nothing to do with each other, however it does look like the fuse and relay box is included in the same circuit as the cooling fan control module.

At this point I'm pretty sure there is no fuse for the cooling fan control module, but I am guessing there has to be a relay in there somewhere that does switch it on.

I guess come this weekend, I'll do some testing on the relays and double check all the fuses.
 

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Discussion Starter · #17 ·
Mike any progress?
No really, I realized that I don't even know when the fan is suppose to kick in, even at low RPM. Unless someone could help me out and see if the radiator fan turns on even at normal operating temps with the heater blower off, then I'll know if I'm looking for nothing.

As it stands I put in a new ECT sensor and it seems as if this one shows lower temps on the gauge then the previous one.

Thanks,
Mike
 

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Discussion Starter · #18 ·
So at this point I have no clue what could be wrong,the radiator fan runs when heating in the car is turned on with the EC off but that's about it.

One thing I did retest is the fan speed, and it is not turning as weakly as I made it seem at first, I guess its just the right RPM for when you have the EC turned off since that's when AC operates as well.

I am down to two things being wrong, either there is still something not working properly with my K40 relay even though I re flowed all the soldering connections and the car started working much much better.

Or the AUX Water pump located in the bottom right area of the front bumper/fender has something to do with it but I highly doubt because I went through the wiring schematics over and over and none of those two circuits mix anywhere together so I'm pretty much scratching this off hehe.

So I am left with two solutions, buy a new K40 relay control module for $200 bucks and hope that works or but a flex-a-lite variable fan control module and just say **** to the stock cooling system and run my own.

I would prefer if I could get it working with out making my own wiring which is not that big of a deal and I'll know it's done properly not some Mercdes gimmick hehe, and buying a new k40 at 110k miles might not be a bad idea even though my unit looks pretty damn good for its age.

Any suggestions would be great, otherwise next week after payday I'm buying two new o2 sensors and the flex-a-lite kit hehe. I could probably use the Flex-a-lite kit on some of my other projects anyways if I figure out the issues with the stock setup hehe.

Thanks,
Mike
 

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Discussion Starter · #20 ·
Since your not sure it's broken, don't fix it. I think I would wait and see if the car does OK in the summer.
At this point I'm about 99.99% sure its not working as intended. I fail to believe that no matter what specs MB builds their motors to.

That when the heat gauge hits 110c at idle and standing still the fan doesn't even kick on into low mode with the EC button turned on of course.

When the EC button is set to off the fan runs constantly at low mode because it pretty much runs the AC at the same time as well so its auto on.

Its been hitting 60f - 70f degrees last few days here, and the car at idle and standing still (Obviously hehe) hits at least 100c pretty quickly.

I have blown many head gaskets in my life to know that temps is no good for any i4 motor HAHAHA.

Unless someone can confirm that their fan doesn't run at all when their car hits 100c at idle and standing still with ec light on, than I am considering this a defect. :)
 
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