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Almost a month ago the cooling fan behind the radiator started working consistently on highest speed possible, as if it's a jet engine !
Went to couple of local workshops, hooked the car up to a computer but no fault codes, another guy did the some diagnosis the old school, and he concluded that the resistor of the fan is faulty.
I have been trying to find a resistor for this fan, according to original Mercedes drawings and diagrams, the whole fan is supplied as one whole assembly, assumingly the resistor belongs to that assembly, needless to say, that fan costs a fortune, 600 USD at my local dealer + labor...
moreover, through one thread that I read before, the always on fan is usually caused by a faulty refrigerant pressure sensor that tends to fail in this model, however it was said that to test the pressure sensor, disconnect it, and if the fan stops then the sensor is faulty, if the fan doesn’t stop, the sensor should be healthy, which is my case... it might be worth mentioning that the AC is cold as it should be, no refrigerant pressure loos, but the fan is still on even when it is 7 degrees outside with a cold start.
I would like to hear if any of you have got similar issue with that resistor before and how it was solved,
Any thoughts around this will be appreciated
Faulty engine control module is also another possibility. Stay away from this old school mechanics. The fan on your vehicle does not have a resistor box. It has a controller module, which is not available separate. The way it works, it gets a signal from the engine control module as a request for fan speed. The signal is under 5volts.
Hi there, thanks for replies and suggestions...
actually the fan is on even if I stop the AC, it startes anyway like 15 sec. After the engine turns on,
regarding the engine coola t temp sensor, do you know how I can diagnose? Or where is it located? Any hint, pic, article number can be useful
I am also having this same issue with my 2011 E550. Fan turns on immediately after start up and is very loud and annoying to say the least. Can't find any threads searching Google in regards to the w212 chassis and fan issues so it makes it that much more frustrating. I bought a coolant temperature sensor today but cant find the location on my motor. Any help would be greatly appreciated.
I am also having this same issue with my 2011 E550. Fan turns on immediately after start up and is very loud and annoying to say the least. Can't find any threads searching Google in regards to the w212 chassis and fan issues so it makes it that much more frustrating. I bought a coolant temperature sensor today but cant find the location on my motor. Any help would be greatly appreciated.
If you have the M273 motor (non turbo) the coolant sensor is a pain to remove. It is located on the driver's side cylinder bank, at the rear of the engine, right under the plastic freeze plug. I was going to post a DIY on it when I had some time. I'll just post a few pics with some pointers.
You'll need a pick to pull the plastic locking tab on the sensor plug so it can be removed. Getting to that Torx is the worst part, wear a long sleeve shirt that can protect your wrist and arm skin, there are sharp edges on the engine casting in that area. Depending on how fast you move when installing the new sensor, you might lose more or less coolant. I only lost about 100 ml. You can replace that with distilled water if you don't waste more than 250 ml.
My temp sensor was intermittently failing so there were no errors to be found with generic scan tools. I was able to find it with Xentry and my C4 clone. The symptoms were identical to yours + misfiring& rough running when the engine was cold.
Good luck and let us know how it went.
If you have the M273 motor (non turbo) the coolant sensor is a pain to remove. It is located on the driver's side cylinder bank, at the rear of the engine, right under the plastic freeze plug. I was going to post a DIY on it when I had some time. I'll just post a few pics with some pointers.
You'll need a pick to pull the plastic locking tab on the sensor plug so it can be removed. Getting to that Torx is the worst part, wear a long sleeve shirt that can protect your wrist and arm skin, there are sharp edges on the engine casting in that area. Depending on how fast you move when installing the new sensor, you might lose more or less coolant. I only lost about 100 ml. You can replace that with distilled water if you don't waste more than 250 ml.
My temp sensor was intermittently failing so there were no errors to be found with generic scan tools. I was able to find it with Xentry and my C4 clone. The symptoms were identical to yours + misfiring& rough running when the engine was cold.
Good luck and let us know how it went.
How did you remove the temp sensor?? I tried last night for an hour and no luck. It's a wierd looking plug and can't seem to figure it out. So frustrating trying to do stuff on these motors.
The two sensors( temp& crank position) are held together by a metal bracket which is bolted to the block via the Torx screw I mentioned before. Remove the screw first, the bracket comes off and then you can use a pick to pull the locking tab on the temp sensor plug back so you can pull it (unplug). After that you can remove the temp sensor, it comes out easily.
If I remember correctly you might have to remove the CPS ( Crank position sensor) to be able to pull that metal bracket. The CPS has a plastic tab you'll need to pull to be able to unplug it. Feel for the locking tab of the CPS I don't remember exactly where it was(I think it's on the underside of the plug itself, not visible from the top). I too was annoyed by this, had to figure it out by myself.
That's the plug that's got me stuck. I could hear a slight click when I pushed on the underside but it wouldn't come off when I pulled on it. If it's a tab as you say I would have to pull on that tab. Thanks for all your help.
Just finished the coolant temperature sensor replacement and what a PIA. That is definetly one of the harder jobs to do on this thing because everything is blind and by feel only. If anyone does attempt it the torx bolt was a T30. Not sure if it fixed my problem or not at the moment going to take a nap lol and give it a day of normal driving. Fan does sound quieter but could just be me.
Well it is finally fixed. After buying a real scanner I could pull the code from my front SAM and it was the AC pressure switch. Changed it out and viola the fan isn't running all the time. Anyone with this issue on a w212 I would recommend you start here.
Hi Do i understand you went to all that effort to change the water sensor and it wasnt at fault, the cause of the cooling fans to be on al the time was the air con pressure switch
I Have a W166 2014 ML63
my cooling fans come on about 10 seconds after start up and stay on. full blast . (ambient 19 Celsius /66 Fahrenheit ) air conditioner is OFF (although the fresh air vent blower was on) I noted the Green start / stop light was no longer lit on my dash. (no ECU light or any other unusual light lit up) I noticed the temperature gauge was down low/cold and after 5 minutes of driving the temperature was back to normal but the fans are still on full blast. I stopped for 15 minutes then started up and again temp was low/cold but built up quick after 5 minutes of driving, fan still on full blast. car seams to be running fine, and the transmission is hanging onto gears a little longer than normal
fitted the iSoft MB OB2 analyser result is P050C64 "the coolant temperature of the combustion engine is implausible during a cold start. there is an implausible signal " Control Unit MED177_M157-CAN MB number 2789011300 P050C Cold Start Engine Coolant Temperature Performance (obd-codes.com)
dealer suggests there has been a lot of problems with the resistor in the fan Anyone with any wisdom they can share?
SOLUTION PENDING. for those interested or who may come up with the same problem.
I was all prepared to replace the coolant temperature sensor and when i went to put the car up on the ramps to start work HEY PRESTO problem was gone.
WHAT DID I DO?? removed the left air filter to do some investigation as to the location of the coolant temperature sensor (located below the left hand head)
ALSO pushed the connector to the fan which was in place (but the moving of the connector I believe was the solution) this indicates potentially a poor connection at the plug and probably result in a reoccurrence of the problem.
SO if this problem occures again , hopefully i know where to look, I put the OB11 analyser on to check codes and noted the fault codes had cleared.
Well it is finally fixed. After buying a real scanner I could pull the code from my front SAM and it was the AC pressure switch. Changed it out and viola the fan isn't running all the time. Anyone with this issue on a w212 I would recommend you start here.
Hello,
Can you share where the AC pressure switch is, and if it’s able to be changed by user or workshop? Thanks!
Hello,
Can you share where the AC pressure switch is, and if it’s able to be changed by user or workshop? Thanks!
Sensor is located on the condenser. You'll need A/C tools such as vacuum pump, (scale) and a gauge set to replace that sensor after you get the existing load safely recovered.
I have a similar issue where the fan is on all the time.
I've taken to a garage and the diags kit showed a faulty AC sensor.
They've ordered one but advised the AC will have to be de-gassed before replacing the sensor and then re-gassed after being fitted.
I just wanted to check if this has to be done as re-gassing will be over twice the price of having the sensor fitted.
Can anyone confirm this has to be done?
Thanks in advance
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