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I searched, and could not find an answer for this.

My 2001 C320 was overheating. After reading here, and doing some diagnostic work, the fuse was a little burnt. Replaced that, and still no luck. Then I did the A/C trick, and the fan came on, but at slow speed.

So I'm guessing it's the temperature sensor or the relay. Process of elimination, where is the relay? None of the books, or schematics tell me.

Thanks
 

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2004 CLK 240 Coupe
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So I'm guessing it's the temperature sensor or the relay. Process of elimination, where is the relay? None of the books, or schematics tell me.
The reason that nobody could tell you where the relay is located - is because there isn't one!

The electric suction fan (engine & a/c) with integrated control (M4/7) is driven from ME-SFI control module [ECU] N3/10. It is protected by fuse f5 (125A) located in Front pre-fusebox F32.

Initiation is from the coolant temp sensor (B11/4) but fan speed variation is managed within M4/7.
 

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2007 C230 Sport
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My 07 c230 had cooling/ fan issues earlier this year. The fan quit, then worked again. The next day it ran at 100% all day and sounded like a jet taking off. It then stopped working then started again. I found a lot of complaints about the fan module failing which is built in to the fan itself. So $450 later I installed a new fan and all works fine. Hopefully this helps.
 

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2004 CLK 240 Coupe
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Interesting. Sadly I haven't heard of folks 'repairing' this module, so I guess that failures are quite unusual.
 

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2007 C230 Sport
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MB dealer in Daytona Beach has sold a bunch of fan assemblys and I found a lot of info by google as well. The independant shop I use has replaced several as well. What did you actually find with yours?
 

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01 c320 w203 sedan v6 3.2l
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01 c320...Is the cooling fan supposed to come on right when you start the , car, or does it take time ???
 

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CURRENT: 2011 SL550 FORMER: C300, ML350, CLK550 Cabriolet, C240, ML320, 300TD
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It only comes on when needed, such as when idling and the engine temp climbs, or when running the AC.

Here's a full fuse and relay chart:

 

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01 c320 w203 sedan v6 3.2l
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The fan doesn't come on w the ac so I checked the voltages across the 4 pin fan connector...with the car on, 1 of the smaller wires (grn/blu) is only at .3 volts..the other 2 at 12v and the brown is ground.. is .3 volts normal? When I bypass the .3 volts w/ a 12v source the fan comes on super fast...please help...
 

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CURRENT: 2011 SL550 FORMER: C300, ML350, CLK550 Cabriolet, C240, ML320, 300TD
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The fan is controlled electronically by the ECU, and since you have voltage, it's not the relay or fuse. If the fan were not working, you should get an MIL (check engine light). My guess is that it's not getting hot enough or the AC is not need enough airflow across the condensor to need the fan. How hot does the engine get? If it goes over 90C, the fan should definitely be running.
 

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Hello.. So I have a 2003 C-320. Before I start the car (in the 2nd key position) my fan turns on (and when the car starts the fan continues on) at 100%, I used the icarsoft data and nothing calls for the fan to run. I have several error codesB1042, B1048, B1055, P2401 & 2402, P2310, 2311, 2312, 2315 and P2600... I just replaced the light control switch (as the previous owner cut the wires), and the front headlights and "city" lights work well, but I am missing the front right marker lights (as in it is not there at all), and the left one sometimes works, sometimes nope. I understand that there may be more than one issue, but any advice of a fan that just runs for no reason? Thank you!!!!!
 

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2008 ML350 (Me!), 2010 GLK350 (Wife), 2003 ML-350 (Deceased)
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Those are generic codes which can mean multiple things for different brands of vehicles. Just a guess, but it is most likely related to code P2600, which can mean (among other things) that your auxiliary coolant pump has failed. Maybe since it isn't working, the system goes into "always on" mode as a precaution?
 

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Those are generic codes which can mean multiple things for different brands of vehicles. Just a guess, but it is most likely related to code P2600, which can mean (among other things) that your auxiliary coolant pump has failed. Maybe since it isn't working, the system goes into "always on" mode as a precaution?
Thank you.. I checked the pump, the wiring is good both negative to the ECU and positive, under direct power, the pump works, but nothing is telling it to turn on... Also, bad news for me, when I put the pump under direct power, I hear girgling of water by the flow sensor and car has antifreeze under it.. but I still don't know why the fan is always running even if I don't start the car. I just changed the Temperature Control Sensor, no change.
 

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W163 Crash Test Driver
2008 ML350 (Me!), 2010 GLK350 (Wife), 2003 ML-350 (Deceased)
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I dug up some more info for you. Scratch my guess earlier about the aux pump. ;)

There are several modules and a sensors that all work in concert to regulate the fan speed (see attached). The coolant sensor is just one of them. It also looks at A/C refrigerant pressure and the outdoor ambient air sensor as well. Both the ECU and the climate control modules can directly control the fan and it's speed. The fan itself is intelligent and has it's own module as well.

Any one of the devices in the attached doc could be at fault. But you have bigger fish to fry. Before throwing parts at it, I would fix all your other codes first and see if the fan still runs at 100% continuously. It would also help you greatly if you could scan with a Mercedes savvy scanner that can read all modules.
 

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I dug up some more info for you. Scratch my guess earlier about the aux pump. ;)

There are several modules and a sensors that all work in concert to regulate the fan speed (see attached). The coolant sensor is just one of them. It also looks at A/C refrigerant pressure and the outdoor ambient air sensor as well. Both the ECU and the climate control modules can directly control the fan and it's speed. The fan itself is intelligent and has it's own module as well.

Any one of the devices in the attached doc could be at fault. But you have bigger fish to fry. Before throwing parts at it, I would fix all your other codes first and see if the fan still runs at 100% continuously. It would also help you greatly if you could scan with a Mercedes savvy scanner that can read all modules.
Thank you.. I have the icarsoft, i980, shows no errors with fuses or relays. I think there is a short because the rear tail light is also not working, and front drivers side marker light either, has like 980 MV. The "City" lights are dim and an LED bulb just blinks (as not enough power to get it going).

This MAY have nothing to do with the fan, but who the heck knows. There was sitting water under the battery, the stupid drain was clogged with the protective foam that now dry rotted. I just finished cleaning that out.. I thought maybe water, and wires going though may have been the issue, but I found nothing yet.

Thank you again!!! I have to keep looking..
 

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Coupe/Convertible Forums Moderator
CURRENT: 2011 SL550 FORMER: C300, ML350, CLK550 Cabriolet, C240, ML320, 300TD
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LED blink because of the circuitry used in the SAMs to detect bad/blown bulbs. The external lighting is electronically controlled by the SAMs. Instead of fuses to protect the circuits, the SAMs an detect current draw and will shut down a circuit that draw too much or too little current. LEDs draw less wattage than incandescent bulbs, and the SAM registers that as a blown bulb. It will "blink" the circuit a few times to test it, then it shuts it down if the current draw is not correct.
 
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