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Can anyone please share the circuits diagram for the radiator fan operation and components?
The issue I have is that the radiator fan starts as soon as the ignition switch is placed on the run position even if the car is not started and have been parked overnight. It running full speed when driving and continue to run for about a min after the car is turned off, then the fan stops.
this condition is the same if the AC is on or off. There are no codes on the ecu, ac, Sam, or any other unit that my iCarsoft CR Pro could read except for the intake manifold flap code which has been there for ever without triggering a check engine light.
so far, I have replaced the thermostat which includes the coolant temperature sensor in the same unit for this car. I swapped the complete radiator fan with another fan from a working car with no change. I also cleaned and swapped the MAF sensor and no change. I removed relay O from driver SAM as someone listed it as the Fan Relay but the fan continues to run. Not sure which relay truly controls the fan? I disconnected the Refrigerant pressure sensor then I got error codes on my scanner and the ac stopped giving cold, so I plugged it back and all is well with AC but the fan still running. The engine oil has been serviced less the a 1,000 mile ago and still good. The signal wire to the fan reads about 3.5v when the big fan plug is disconnected from the fan, but back propping the same wire is about 11.5v when the fan is plugged and running at full speed.
Is it true that the Dash Climate control panel could be at fault and needs replacement ? This is the only lead I have for now. I have a spare ECU but is need programming to my car before I can swap ECU and that is another expensive option that I want to keep foe last. In case I have to replace the ECU, I would appreciate a recommended outlet that can program the new one using the existing ECU only.
I hope someone gives me a lead to fix this issue before the fan dies from being over worked.
As I mentioned in the original post, it was strange that even when I pulled out Relay O the fan kept on running so I asked if it could be another relay. What do you make of that? I also swapped relay O with another relay with the same numbers, and no change in the fan behavior !
Thanks konigstiger for the attachments and your feedback in this issue. Definitely much appreciated.
From reading your 3rd attachment “Engine and AC electric suction fan with integrated control, function”, I see that signals from N22/AAC i.e. Climate control panel in the dash AND N3/10 i.e. the ECU are sent on the signal wire to the M4/7 i.e. the Fan brain to determine the fan speed. Unfortunately, I do not have a scope to read the signal wire. Only a multimeter.
The sensors input such as engine coolant temperature and refrigerant pressure play a big factor in that signal. The coolant temperature gauge seems to display normal starting temperature at cold start and rises up as the car get warmer stopping around 80 C even before I installed the new Thermostat housing which includes the sensor in the same unit. As for the refrigerant pressure, I have been having a small leak in the refrigerant in past 3 year so I add a can (12oz) of refrigerant every summer. The code reader displays the refrigerant pressure and voltages as follows:-
AC is Off
Current consumption of component A9(Refrigerant compressor) ----- 0mA
On/off ratio of component A9(Refrigerant compressor) ----- 0%
B12(refrigerant pressure sensor) ----- 72.52psi ~~ almost 5 Bar.
AC is On lowest temperature blowing around 40 F air out of the vents with 85 F weather outside.
Current consumption of component A9(Refrigerant compressor) ----- 700mA
On/off ratio of component A9(Refrigerant compressor) ----- 70%
B12(refrigerant pressure sensor) ----- 101.53psi ~~ almost 7 Bar.
So my take is the pressure is below the 12 bar and the fan should be running in basic venting YET it is running at full or almost full speed and sound like an airplane taking off!
I was going to vacuum the AC system, replace the pressure sensor and then recharge it but I thought that would be a waste of refrigerant. Could it be a bad sensor with the above readings? I do not have a base to compare the reading I got to what is normal.
Once I replace the N22/AAC I will update the post with the outcome. In the meantime, I’m open for suggestion and leads on what to try.
p.s. Thanks for the pre-fuse documents; I will be looking for corrosions and loss connections in that area but the fuse have to be good since the fan is running. Right?
Thanks for the info bmwpowere36m3. I have seen this before and that is where I got the idea that it could be a bad ECU but I'm saving this step for last since it will cost hundreds to reprogram the ECU by an expert. Beside this guy's website is business where you have to pay a minimum of 20 dollars just to get the contact information for his guy Mike that reprogramed his ECU at GOD knows how much??? I tried to tap on my ECU but unlike his case, the voltage did not change on the signal wire. So I'm hopping its not the ECU.
Nice find! I bet that ECU wouldn't have failed if it wasn't mounted on top of the hot vibrating engine it's entire life. What a daft idea.
Definitely a prioritization of modular assembly... on the W212 there's lots of them, certainly making assembly at factory easier. Whether its the rear subframe (diff, axles, links, brakes) front subframe and engine, inner door panels (lock mechanism, window regulator), etc..
Thank you for the wiring diagram . Looking at live data for the ac control using my scanner, I just noticed the B12/2 pressure and temperature sensor is giving a crazy (-146.2 F) temp reading so I ordered a new oem sensor and should get it by next week. I will be recovering the refrigerant and recharging the system with oil, die, and rR134a after installing the new sensor. Will update as condition change.
update: so I got the new sensor from eBay for $32 that have the part number and Mercedes logo engraved on it but it could be a fake… before I vacuum the system I connected the new sensor and scanned for codes. Of course the pressure was 0 psi and the AC did not work but the problem was that the temperature was still -146.2 F / -99 C.
My question is: could this give the ECU the wrong input and cause it to turn the fan on full speed? Are the 2 sensors I tested the same way above are both bad or is it a wiring issue?
it will be great if some one can share the pressure / temp sensor wiring diagram and where the temp feedback signal connect to in the ECU?
W211 2004 E500 Wagon
I noticed the same symptom in the last couple days. My E wagon sounded like a non-stop jet engine shortly after I replaced a disintegrated serpentine belt with an A/C bypass belt while I wait for the AC compressor mag/pulley. At first, I thought something among the ECU-like components was tripped. As it became increasingly annoying and I began to think it was bad for my cooling fan motor, I recalled how much I "jostled" the wiring around the fan as I used a long torque wrench to turn the tension pulley bolt (just as a convenience since the socket handle was so long). On a whim, I popped the hood and jiggled the wiring at the very front of the engine bay adjacent the fan (more to the passenger's side slightly). Closed the hood, started the car and I was no longer a jet engine.... I had also noticed during the non-stop high speed cooling fan period that the E wagon was running a little cool (as expected I guess). So to conclude, I assume I have a wiring issue that I will investigate when I attempt to install the A/C pulley. All comments made here should be read with my qualifications in mind . . . I am fully qualified to have my own "how not to fix things" yutube channel. Still after reading this thread I thought I would add my experience with just jiggling the wires. . . I don't see how or why or short or a break in the wires, even at a connector, could result in a non-stop max speed fan without trigging some kind of dashboard message but that is what happened. My experience suggests the wiring and/or connectors could be the cause. Regards and thanks for a great post . . . and it remains impossible to thank K for all the posts I have learned from.
PS - I judge the probability I will get the A/C pulley installed in the 10 to 15 percent range. It will be warm here by next weekend and wish to avoid crawling to the mechanic on my knees . . . he will no doubt insist on a knew compressor, etc. $$$$ and anything else that will damage my pride.
Last edited by sweseman; 07-16-2021 at 09:45 PM.
Reason: To add another joke
When this happened to me, radiator fan spinning like crazy with no reason whatsoever as soon as I start the car (2004 e500 4M), all I had to do was disconnect the trunk battery for 30minutes and the problem was solved. Fan went back to working properly again.
These cars are like that, they need a hard reset (if that’s the proper term) when oddities come up.
Last edited by AlmostHappy; 08-02-2021 at 12:00 AM.
Thank you for the wiring diagram . Looking at live data for the ac control using my scanner, I just noticed the B12/2 pressure and temperature sensor is giving a crazy (-146.2 F) temp reading so I ordered a new oem sensor and should get it by next week. I will be recovering the refrigerant and recharging the system with oil, die, and rR134a after installing the new sensor. Will update as condition change.
update: so I got the new sensor from eBay for $32 that have the part number and Mercedes logo engraved on it but it could be a fake… before I vacuum the system I connected the new sensor and scanned for codes. Of course the pressure was 0 psi and the AC did not work but the problem was that the temperature was still -146.2 F / -99 C.
My question is: could this give the ECU the wrong input and cause it to turn the fan on full speed? Are the 2 sensors I tested the same way above are both bad or is it a wiring issue?
it will be great if some one can share the pressure / temp sensor wiring diagram and where the temp feedback signal connect to in the ECU?
Hi Mario,
Where was the problem, did you solve it ?
In my case after I checked everything it is 99.9% the ECU signal to the fan which means to replace or clone my ECU with a “good” used ECU but both options are expensive. It has been difficult to find a shop to do that in my area. So I’m living with the loud noise of the fan and have a backup fan I picked up from the junk yard in standby just in case this one dies.
thanks for posting this. My mechanic went through 2 aftermarket fans and one oem used fan and my fan was still running full speed at random times. I bought a used ecu from ebay and sent it to the guy Mike in NY for cloning and its working great now. I got Mike's info from the YouTube guy that posted this video (master tech Lou)
Can anyone please share the circuits diagram for the radiator fan operation and components?
The issue I have is that the radiator fan starts as soon as the ignition switch is placed on the run position even if the car is not started and have been parked overnight. It running full speed when driving and continue to run for about a min after the car is turned off, then the fan stops.
this condition is the same if the AC is on or off. There are no codes on the ecu, ac, Sam, or any other unit that my iCarsoft CR Pro could read except for the intake manifold flap code which has been there for ever without triggering a check engine light.
so far, I have replaced the thermostat which includes the coolant temperature sensor in the same unit for this car. I swapped the complete radiator fan with another fan from a working car with no change. I also cleaned and swapped the MAF sensor and no change. I removed relay O from driver SAM as someone listed it as the Fan Relay but the fan continues to run. Not sure which relay truly controls the fan? I disconnected the Refrigerant pressure sensor then I got error codes on my scanner and the ac stopped giving cold, so I plugged it back and all is well with AC but the fan still running. The engine oil has been serviced less the a 1,000 mile ago and still good. The signal wire to the fan reads about 3.5v when the big fan plug is disconnected from the fan, but back propping the same wire is about 11.5v when the fan is plugged and running at full speed.
Is it true that the Dash Climate control panel could be at fault and needs replacement ? This is the only lead I have for now. I have a spare ECU but is need programming to my car before I can swap ECU and that is another expensive option that I want to keep foe last. In case I have to replace the ECU, I would appreciate a recommended outlet that can program the new one using the existing ECU only.
I hope someone gives me a lead to fix this issue before the fan dies from being over worked.
Finally, did you solve the problem, I'm in the same type of failure
07-06-2021, 07:29 AM
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