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  #11  
Old 08-03-2014, 10:50 PM
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Sounds like it needs a recode - someone has done a swapsies
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  #12  
Old 08-03-2014, 11:25 PM
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Magnet inside is misaligned?
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E53 X5 4.6iS
147K mi - Sold May 2013
Tireprints left in:
USA, Nicaragua, Costa Rica, Panama, Russia

E53 X5 4.8iS built 2005-10-17
66200 mi - June 2012
96000 mi - June 2013
112000 mi - June 2014
OEM fire extinguisher
OE first aid kit
OE tow hitch
OE TV module
OE aspheric mirror
K&N air filter
black/white badges
rear camera
4-channel video recorder

Here is the list of things I have done to the X
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  #13  
Old 08-05-2014, 03:39 AM
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Thanks for the continuing interest and replies. Bulk – can you please elaborate on what you mean by a “swapsie”?? As I mentioned, I replaced the tank and sensor with new, correct parts. How can just replacing these plug-and-play components affect or swap anything? Did I fail to do a procedure with the computer or something and the signal from the sensor lead wires got “swapped”? I’m a bit lost on what you are referring to. The reverse behavior I am seeing shouldn’t be caused by simply plugging in a new sensor, and there is only one way to plug it in.

Also, to do the “recode” – I assume you are referring to setting some flag somewhere – or “unswapping” whatever happened to begin with. Can you provide some detail? What is the parameter name and value and would I be using a GT1 or other software?

Terminator – you made me realize there is a test I could do; I could drain the expansion tank such that the float goes to the bottom and see if that makes the message go away. That would at least prove that there is indeed a magnet on the float and is working “properly” albeit backwards.
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  #14  
Old 08-13-2014, 03:36 PM
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I just fixed this problem two weekends ago.

I did a complete coolant hose/waterpump job in December. And like many suggest, I also purchased a new Expansion tank.

From day one, I was getting this error. I checked the wiring over and over. I tried burping, and setting the water levels high and low, I changed the sensor twice.

Recently, I started leaking coolant out of the lower connector to the EX-Tank. I decided to get a new hose and another expansion tank. The leak went away and the low coolant level warnings did too. Bad tank.
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  #15  
Old 08-13-2014, 07:24 PM
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Thanks for sharing your experience. So a "bad tank" really means that something is bad with the float system. I wonder if some of these aftermarket tanks are made without the magnet in the float? I mean a poor job of reverse engineering (instead of using a specification) would be to measure the tank dimensions and put a float in, but unless you really understood how the system worked, you would not embed a magnet in the float. Maybe that's it. The manufacturer would probably not get enough complaints to understand their tank was faulty since as we can see from the thread, figuring out why we get the message is not easily obvious. Just a theory...
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  #16  
Old 06-28-2017, 09:53 AM
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permanent "check coolant level"message-how sensor works ?

Hi everyone,
It seems this is a long overdue explanation for how the coolant level sensor works on BMWs...
Everyone seems to agree the sensor is a reed relay that gets triggered by the magnet on the floater,the magnet on the floater causing the reed relay to close, right?!Only partially correct- But then, if the sensor is out of the dry-well or if the connector is disconnected, the "check coolant message" becomes permanent, also if the connector pins are shorted ( with a staple or something else), the message goes away!!! This seems to be "backward " !! So the explanation is simple:
The sensor should be "normal closed"- no check coolant message ! They achieve this, by having a SECOND magnet on the dry well !!!! This causes the reed relay( coolant level sensor) to close AS SOON inserted on the dry well! ( tested by me on an OEM tank). Now when the coolant level drops and the floater gets close to the reed relay, the magnetic field from the magnet on the floater will counter-effect the one on the dry well( sensor enclosure) to open up the relay= check coolant message !
This is how it works ! and this is why many after market expansion tank will throw this "check coolant level" message !- they don't have the second magnet on the dry well to keep the relay closed in normal operation !
OEM expansion tanks can fail also ( probably by this second magnet getting either loose or weak with the time- not being able to keep the relay closed in normal operation= coolant level OK, or by floater magnet falling on the bottom of the tank and counter effect the magnet keeping the sensor closed)
I hope this helps everyone understand once for all how this wicked system works!
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  #17  
Old 06-29-2017, 11:56 PM
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Quote:
Originally Posted by Clutch View Post
Thanks for sharing your experience. So a "bad tank" really means that something is bad with the float system. I wonder if some of these aftermarket tanks are made without the magnet in the float? I mean a poor job of reverse engineering (instead of using a specification) would be to measure the tank dimensions and put a float in, but unless you really understood how the system worked, you would not embed a magnet in the float. Maybe that's it. The manufacturer would probably not get enough complaints to understand their tank was faulty since as we can see from the thread, figuring out why we get the message is not easily obvious. Just a theory...
If your sensor is reacting to the magnet ex situ, the tank is likely bad. Try another aftermarket tank, or fix it the first time and buy a genuine BMW tank from an online vendor.
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  #18  
Old 09-21-2017, 03:45 PM
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Quote:
Originally Posted by Clutch View Post
Thanks for sharing your experience. So a "bad tank" really means that something is bad with the float system. I wonder if some of these aftermarket tanks are made without the magnet in the float? I mean a poor job of reverse engineering (instead of using a specification) would be to measure the tank dimensions and put a float in, but unless you really understood how the system worked, you would not embed a magnet in the float. Maybe that's it. The manufacturer would probably not get enough complaints to understand their tank was faulty since as we can see from the thread, figuring out why we get the message is not easily obvious. Just a theory...
Hi there, I know this tread is very old but how did you resolve the issue? Thanks..
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  #19  
Old 09-22-2017, 01:37 PM
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Quote:
Originally Posted by flaviu View Post
Hi everyone,
It seems this is a long overdue explanation for how the coolant level sensor works on BMWs...
Everyone seems to agree the sensor is a reed relay that gets triggered by the magnet on the floater,the magnet on the floater causing the reed relay to close, right?!Only partially correct- But then, if the sensor is out of the dry-well or if the connector is disconnected, the "check coolant message" becomes permanent, also if the connector pins are shorted ( with a staple or something else), the message goes away!!! This seems to be "backward " !! So the explanation is simple:
The sensor should be "normal closed"- no check coolant message ! They achieve this, by having a SECOND magnet on the dry well !!!! This causes the reed relay( coolant level sensor) to close AS SOON inserted on the dry well! ( tested by me on an OEM tank). Now when the coolant level drops and the floater gets close to the reed relay, the magnetic field from the magnet on the floater will counter-effect the one on the dry well( sensor enclosure) to open up the relay= check coolant message !
This is how it works ! and this is why many after market expansion tank will throw this "check coolant level" message !- they don't have the second magnet on the dry well to keep the relay closed in normal operation !
OEM expansion tanks can fail also ( probably by this second magnet getting either loose or weak with the time- not being able to keep the relay closed in normal operation= coolant level OK, or by floater magnet falling on the bottom of the tank and counter effect the magnet keeping the sensor closed)
I hope this helps everyone understand once for all how this wicked system works!
Thanks for the excellent research and explanation. This seems to fill in all the mysteries in the rest of this thread. I'll try to remember it if I ever have any problems.
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  #20  
Old 10-19-2018, 07:09 AM
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Quote:
Originally Posted by Qsilver7 View Post
You don't mention if you checked the coolant level sensor...which is not the "float" that you see when you undo the tank's lid (yes, it does fool many owners).

The sensor is screwed in from the bottom and is probably in a "dry" well (if like the expansion tanks since the m60-m62tu engines.

See #3 in the diagram below...and also check if the electrical harness (#6) is plugged in correctly to the sensor:

For example, in the pic below of an e39's expansion tank split open...you can see the float (it's goldish-tan in the 1st pic) in its normal "full" location inside the tank...and the "level sensor" is sitting to the far right (just below the split-opened tank). Again, the level sensor screws up inside a dry well in the tank...which is near the bottom of the float mechanism inside the tank. You can also see a "staple" sitting on a circular magnet in the bottom part of the float. I believe magnetism is somehow used to communicate the level of fluid in the tank to the level sensor. As the fluid lever drops inside the tank, the float lowers closer to the level sensor...and when the low point is reached, the proximity of the bottom of the float to the level sensor triggers the warning (see the 2nd image below):

(all images below: courtesy of Bluebee)





In this last image below...you can see that the internal "float" is at the very bottom of its range as if the tank was empty...you can see that the bottom half which contains the magnet...is also surrounding the "dry well" that the level sensor is screwed into...thus my assumption that the magnet is how the coolant level sensor recognizes that the tank is not full.

If for some reason your level sensor has gone bad...or the bottom half of your float is still down near the level sensor (are you sure your float is intact)...you need to check the coolant level sensor or its electrical harness.




It just amuses me to see how many people don't know what or how a magnetic reed switch works. The Magnet operates the reed switch which is the coolant level sensor. It operates like a door alarm switch where you have a fixed magnet and a fixed switch. As the magnet gets into the proper proximity of the switch it either opens or closes the switch depending on if it's a NC or NO switch. Pretty easy circuit to understand. So it's not the magnet that is communication with the system but the magnet is operating the reed switch that then tells the system if the coolant is low or okay.
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