Electric fan randomly doesn't come on
Thread Starter
Senior Member
Joined: Aug 2009
Posts: 467
Likes: 1
From: Long Island, NY
A few toys & 07' E350 4matic w/AMG sport packg.
Electric fan randomly doesn't come on
Basically that. I've noticed that the electric fan does not come on all the time. It will randomly not turn on with the AC or when the engine temp is rising. The only way to get the fan to come on when it won't on it's own, is to unplug the main connector and plug it back it, and then it works flawlessly until the next random event it decides not to automatically.
I've replaced the fan, since the original fan is about 8 years old, and the magnets on the motor were a bit rusty, for safe measure. Made no difference. A friend of mine has an Autel MaxiSYS computer, and we've ran all diagnostics and computer checks, had a SRS sensor malfunction at the front right corner and a trunk release handle sticking issue, I fixed both, and cleared all codes, let it go for two-three months and we've just checked it and there is NO malfunctions/errors store anywhere in all of the modules. We've even plugged it in while the electric fan was not automatically turning on, and there is nothing. Unplugging the fan during this, shows a fan malfunction, plugging it back in, it shows all is ok.
What do I do? Don't want to bring it to the local dealer since they are incapable of doing honest work. Could the ecu need a software update or reflash? I am thinking it is a software issue at this point. If the ac compressor had a problem (I know the elec fan is governed by the compressor) it would show on the scanner, would it not?
I've replaced the fan, since the original fan is about 8 years old, and the magnets on the motor were a bit rusty, for safe measure. Made no difference. A friend of mine has an Autel MaxiSYS computer, and we've ran all diagnostics and computer checks, had a SRS sensor malfunction at the front right corner and a trunk release handle sticking issue, I fixed both, and cleared all codes, let it go for two-three months and we've just checked it and there is NO malfunctions/errors store anywhere in all of the modules. We've even plugged it in while the electric fan was not automatically turning on, and there is nothing. Unplugging the fan during this, shows a fan malfunction, plugging it back in, it shows all is ok.
What do I do? Don't want to bring it to the local dealer since they are incapable of doing honest work. Could the ecu need a software update or reflash? I am thinking it is a software issue at this point. If the ac compressor had a problem (I know the elec fan is governed by the compressor) it would show on the scanner, would it not?
Out Of Control!!
Joined: Jul 2003
Posts: 15,901
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From: North Scottsdale, AZ
'71 Pinto
Not familiar with Autel MaxiSYS but may be as simple as reading /erasing fault memory with MB DAS. Also consider engine coolant temperature sensor b11/4 located towards the rear on the left cylinder head which transmits to control module n3/10 (front SAM) and in turn to fan m4/7.
Thread Starter
Senior Member
Joined: Aug 2009
Posts: 467
Likes: 1
From: Long Island, NY
A few toys & 07' E350 4matic w/AMG sport packg.
Not familiar with Autel MaxiSYS but may be as simple as reading /erasing fault memory with MB DAS. Also consider engine coolant temperature sensor b11/4 located towards the rear on the left cylinder head which transmits to control module n3/10 (front SAM) and in turn to fan m4/7.
http://www.ecstuning.com/ES2603845/
Thread Starter
Senior Member
Joined: Aug 2009
Posts: 467
Likes: 1
From: Long Island, NY
A few toys & 07' E350 4matic w/AMG sport packg.
I've replaced the coolant temp sensor, car was running fine all day yesterday and then it randomly stopped working again. So it WASN'T the sensor.
Sensor & fan have been replaced now, and the same problem exists.
Sensor & fan have been replaced now, and the same problem exists.
Thread Starter
Senior Member
Joined: Aug 2009
Posts: 467
Likes: 1
From: Long Island, NY
A few toys & 07' E350 4matic w/AMG sport packg.
Not every time. It works perfectly fine, or doesn't, meaning, it will work with AC off and engine getting hot, it will work with AC on, then it will stop doing both.
If I unplug/replug the fan when it's not working but supposed to be, it works as it's supposed to for a while until it starts not working again. That could be an hour later, or a week later, it's never the same.
If I unplug/replug the fan when it's not working but supposed to be, it works as it's supposed to for a while until it starts not working again. That could be an hour later, or a week later, it's never the same.
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Thread Starter
Senior Member
Joined: Aug 2009
Posts: 467
Likes: 1
From: Long Island, NY
A few toys & 07' E350 4matic w/AMG sport packg.
You may be on to something regarding the fan motor voltage----
We know the AC control unit sends a coded 0-100% voltage requirement to the blower regulator and that is based upon many on board sensors to maintain cabin set temps.
We also know that the fan motor voltage is received by the drivers side SAM module and you disconnecting that voltage is read in by the SAM.
My guess is that you wasted loads on money on unneeded parts and you are looking at the wrong component as the fault---I would not buy anything until you have tested the SAM.
We know the AC control unit sends a coded 0-100% voltage requirement to the blower regulator and that is based upon many on board sensors to maintain cabin set temps.
We also know that the fan motor voltage is received by the drivers side SAM module and you disconnecting that voltage is read in by the SAM.
My guess is that you wasted loads on money on unneeded parts and you are looking at the wrong component as the fault---I would not buy anything until you have tested the SAM.
Which SAM should I check? Are you thinking a plug/pin? OBD reader detected no faults...
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Thread Starter
Senior Member
Joined: Aug 2009
Posts: 467
Likes: 1
From: Long Island, NY
A few toys & 07' E350 4matic w/AMG sport packg.
Not familiar with Autel MaxiSYS but may be as simple as reading /erasing fault memory with MB DAS. Also consider engine coolant temperature sensor b11/4 located towards the rear on the left cylinder head which transmits to control module n3/10 (front SAM) and in turn to fan m4/7.
I also took some voltages from the main fan wires...the large red/brown being constant full voltage, and the smaller two (red w/ green & blue w/ green) both gettings variable voltages from 1.5V-13+V depending on HVAC setting. While those voltage feeds are reading, the fan does not switch on.
MBWorld Fanatic!
Joined: Jan 2016
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From: In the Shadow of the Tetons
2013 ML350 Bluetec
How's your ground circuit?
Gotta agree with Plutoe on this one. Sounds like you've got the scratch to invest in your own DAS-Xentry setup. Instead of tossing cash at random parts, get the proper diagnostic tool to find out what's wrong. Or go to a Benz dealer /qualified mechanic and have it checked properly.
Gotta agree with Plutoe on this one. Sounds like you've got the scratch to invest in your own DAS-Xentry setup. Instead of tossing cash at random parts, get the proper diagnostic tool to find out what's wrong. Or go to a Benz dealer /qualified mechanic and have it checked properly.
Newbie
Joined: Jul 2024
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e320 cdi
The electric fan is new, the coolant temp sensor is new, and the fan still randomly does not come on unless I unplug the main plug and plug it back it.
I also took some voltages from the main fan wires...the large red/brown being constant full voltage, and the smaller two (red w/ green & blue w/ green) both gettings variable voltages from 1.5V-13+V depending on HVAC setting. While those voltage feeds are reading, the fan does not switch on.
I also took some voltages from the main fan wires...the large red/brown being constant full voltage, and the smaller two (red w/ green & blue w/ green) both gettings variable voltages from 1.5V-13+V depending on HVAC setting. While those voltage feeds are reading, the fan does not switch on.
