# DEF Tanks Active and Passive Level sensing. From page 91



## Doug Huffman (Apr 25, 2015)

*Level measurement*
There are level sensors both in the active as well as in the passive reservoir. However, these sensors are not continuous sensors as in the fuel system for example. They can determine only a specific point, to which a defined quantity of urea-water solution in the reservoir is assigned.
Two separate level sensors are fitted in the passive reservoir, one for "full" and one for "empty". The signals from the level sensors are not sent directly to the DDE but rather to an evaluator.

The active reservoir contains one level sensor that has various measuring points:
***8226; Full
***8226; Warning 
***8226; Empty.
Also in this case, there is an evaluator installed between the sensors and the DDE, which fulfils the same tasks as for the passive reservoir.

This evaluator sends a plausible level signal to the DDE. It recognizes changes in the fill level caused, for example, by driving uphill/downhill or sloshing of the liquid as opposed to an actual change in the liquid level in the reservoir. Low level is therefore signalled when the corresponding sensor is no longer covered by the urea-water solution for a defined period of time. Once the level drops below this value, it can no longer be reached during normal operation. This means, the liquid sloshing on the sensor or driving uphill/downhill is no longer interpreted as a higher liquid level.

The level measurement system must also recognize when the active and passive reservoirs are refilled. This is achieved by comparing the current level with the value last stored.

The level sensor signal after refilling corresponds to the signal while driving uphill. To avoid possible confusion, the refilling recognition function is limited to a certain period of time after starting the engine and driving off - as it can be assumed that refilling will only take place while the vehicle is stationary.

A certain vehicle speed must be exceeded to ensure that sloshing occurs, thus providing a clear indication that the system has been refilled.
Refilling the system while the engine is running can also be detected but with modified logic. The signals sent by the sensors while the vehicle is stationary are also used for this purpose. The vehicle must be stationary for a defined minimum period in order to make the filling plausible.
When the urea-water solution is frozen, a level sensor will show the same value as when it is not wetted/covered by the solution. A frozen reservoir is therefore shown as empty. For this reason, the following sensor signals are used for measuring the level:
***8226; Ambient temperature
***8226; Temperature in active reservoir
***8226; Heater enable.

*Level calculation*
This function calculates the quantity of urea- water solution remaining in the active reservoir. The calculation is calibrated together with the level measurement.

Every time the level drops below a level sensor the corresponding amount of urea-water solution in the reservoir is stored. The amount of urea-water solution actually injected is then subtracted from this value while the pumped quantity is added.

This makes it possible to determine the level more precisely than that would be possible by simple measurement. In addition, the level can still be determined in the event of one of the level sensors failing.

Since it is possible that refilling is not recognized, the calculation is continued only until the level ought to drop below the next lower sensor.

Example:
Once the level drops below the "full" level sensor, for example, from now on the quantity of used and repumped urea-water solution is taken into account and the actual level below "full" calculated. Normally, the level then drops below the next lower level sensor at the same time as determined by the level calculation. An adjustment takes place at this point and the calculation is restarted.

If, however, a quantity of urea-water solution is refilled without it being detected, the actual level will be higher than the calculated level. The level calculation is stopped if it calculates that the level ought to have dropped below the next level sensor but the level sensor is still wetted/covered.

By way of exception, a defective level sensor can cause the calculation to continue until the reservoir is empty.
https://drive.google.com/open?id=0B1epIteFE7i-aXh5WjdUYmQyX28

*From Page 93 is SCR System Modes, an attempt to describe the logic and control functions.*. It includes the Incorrect Fluid Determination exactly as someone else has described, high downstream NOx despite otherwise normal SCR system functioning. With proper DEF the Incorrect Fluid Determination can only be caused by a faulty sensor or a software fault.


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## Gpw76 (May 15, 2016)

Wow. Great write up Doug!


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## Doug Huffman (Apr 25, 2015)

Gpw76 said:


> Wow. Great write up Doug!


No credit due me, its cribbed entirely from BMW technical documents as a FUQ and credited at the bottom.


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## Gpw76 (May 15, 2016)

Ah, I thought it was a write you did based on information you ascertained. Regardless, thanks for sharing.


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## RPsX5d (Nov 2, 2010)

Doug Huffman said:


> No credit due me, its cribbed entirely from BMW technical documents as a FUQ and credited at the bottom.


This is great information . . . thanks a lot!

I was going to read a bit more but couldn't access the link you included at the bottom. Can you post a few keywords so I can search for that folder/document?

Thanks again.


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## Doug Huffman (Apr 25, 2015)

Advanced Diesel with BluePerformance - 07/2008 PDF by Luca Paindelli at drive.google.com

I just tested it and it worked for me. Now it maybe be slow, a large document, 128 pages with lots of graphics and formatting.

And Luca Paindelli - LPCapital I think - deserves huge thanks for the magnificent resource.


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## RPsX5d (Nov 2, 2010)

Thanks Doug . . . I was doing a cut and paste into the browser (versus clicking on the link) . . .

For cut and paste you need the complete URL . . . 
[url]https://drive.google.com/file/d/0B1epIteFE7i-aXh5WjdUYmQyX28*/view*[/URL]

It turns out I did have a copy of a similar document, very similar, a bit longer . . . here's the version I downloaded . . . unfortunately I can't recall/find where I got it from . . .

Thanks again.


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## 1999BMW (Feb 14, 2010)

*Active Tank Function Unit*

Has anyone replaced the function unit on the active reservoir. If so is there a part # and how did the replacement go??


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## rippjd (Apr 30, 2006)

I figure those that like the level of detail from the OP may be curious to see what ISTA/D shows during a refill. I knew I should be getting close to the 1000 mile "no start" warning, so with ISTA running I queried the Passive and Active tanks under Vehicle Management / Troubleshooting / Function Structure / Power train / Diesel Electronics. There two different "jobs" (ABL) you can run, one for the active tank and one for the passive tank. They allow you to check the actual level being reported. My passive tank was empty, while the active tank was partially filled. These values do not update in real time, so you have to re-run the job to get an updated number.

Next I went to Vehicle Management / Service Functions / Power train / Digital Diesel Electronics to run the SCR Adjustment job. This will show both tanks on the same screen. Again you have to rerun the job to get updates. The last 3 attachments show the initial level, then with 2.5 gallons added, then with almost 5.0 gallons added. After about 1.0 gallon the X5 automatically started transferring DEF from the passive tank into the active tank. In the end I had about a quart of DEF left over.

This was all done with ignition ON, engine OFF. Cheers!


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## BB_cuda (Nov 8, 2011)

:thumbup:Nice stuff there, rippjd! this forum doesn't do rep points so I give them to you in text form


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## Flying Ace (Jan 26, 2015)

rippjd said:


> I figure those that like the level of detail from the OP may be curious to see what ISTA/D shows during a refill. I knew I should be getting close to the 1000 mile "no start" warning, so with ISTA running I queried the Passive and Active tanks under Vehicle Management / Troubleshooting / Function Structure / Power train / Diesel Electronics. There two different "jobs" (ABL) you can run, one for the active tank and one for the passive tank. They allow you to check the actual level being reported. My passive tank was empty, while the active tank was partially filled. These values do not update in real time, so you have to re-run the job to get an updated number.
> 
> Next I went to Vehicle Management / Service Functions / Power train / Digital Diesel Electronics to run the SCR Adjustment job. This will show both tanks on the same screen. Again you have to rerun the job to get updates. The last 3 attachments show the initial level, then with 2.5 gallons added, then with almost 5.0 gallons added. After about 1.0 gallon the X5 automatically started transferring DEF from the passive tank into the active tank. In the end I had about a quart of DEF left over.
> 
> This was all done with ignition ON, engine OFF. Cheers!


so if we don't have the tool you're using, what's the best way regarding when to refill DEF? Wait until the 999 miles to go warning? Do you know the minimum amount of gallons to add to make the 999 go away?

I'm curious b/c I'm about to take a multi-day road trip, and while I haven't gotten the DEF warning yet, I plan on only carrying a single Kruse bottle, will one bottle be sufficient to at least make the warning go away, and then I fill the rest when I get home?


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## floydarogers (Oct 11, 2010)

one 2L container has made my warning go away. I wouldn't even bother carrying one - available everywhere, any parts store, any truck stop.


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## RPsX5d (Nov 2, 2010)

*rippjd* - thanks a lot for taking the time to post this - screenshots were very useful! I always wondered the level of detail ISTA offered. Thanks!

*Flying Ace* - I too have the same question . . . as far as I know, for those of us with no OBD reader or a very basic OBD reader, "wait until 999 message" is our only option. 

I wonder what the Carly OBD reader shows? Can someone with a Carly OBD reader comment? Thanks.

I too wondered about the road trip scenario . . . my *guess* is - half a gallon into the active tank should clear the 999 message . . . I am assuming this because the half-gallon bottle, as I understand it, is a fix for the owner to do before he/she can get to an "authorized BMW dealer".

If I am in your shoes, I will just take the 2.5 gallon can with me and do the DEF refill away from home.



rippjd said:


> I figure those that like the level of detail from the OP may be curious to see what ISTA/D shows during a refill.





Flying Ace said:


> so if we don't have the tool you're using, what's the best way regarding when to refill DEF? Wait until the 999 miles to go warning? Do you know the minimum amount of gallons to add to make the 999 go away?
> 
> I'm curious b/c I'm about to take a multi-day road trip, and while I haven't gotten the DEF warning yet, I plan on only carrying a single Kruse bottle, *will one bottle be sufficient to at least make the warning go away*, and then I fill the rest when I get home?


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## Ozer (Sep 17, 2015)

I highly doubt anyone needs to carry DEF around for trips. Even at the warning you have 1000 miles left. You can find DEF in any decent size gas station. Unless you are going to roam the deserts for 1000 miles... lol


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## Frediesel (Apr 28, 2012)

I carry an empty 2L bottle in my trunk (in case I'm ever far from home) so that I can simply purchase DEF from any vendor in any type of container. I started doing this ever since my light went off weeks before smog testing was due.


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## basilray (Aug 10, 2016)

Frediesel said:


> I carry an empty 2L bottle in my trunk (in case I'm ever far from home) so that I can simply purchase DEF from any vendor in any type of container. I started doing this ever since my light went off weeks before smog testing was due.


I've carried a modified 1/2 liter screw-top for the same purpose as well, but even that is silly. With 1,000 miles of warning travel, it's hard to imagine myself ever really needed to use it over the one I keep in my garage at home, where my DEF is. :rofl:


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## Flying Ace (Jan 26, 2015)

RPsX5d said:


> *rippjd* - thanks a lot for taking the time to post this - screenshots were very useful! I always wondered the level of detail ISTA offered. Thanks!
> 
> *Flying Ace* - I too have the same question . . . as far as I know, for those of us with no OBD reader or a very basic OBD reader, "wait until 999 message" is our only option.
> 
> ...


I guess as others said, it all depends on where you're going. My upcoming trip will be about 300 miles from home, but at my vacation area, l'll only be 60 miles from the nearest BMW or VW dealership, so even if I didn't carry my own Kruse bottle or an emergency fill, I'll be able to make it, but it will be a pain to get there if it snows and will certainly take away from precious vacation time.

To the others that have commented, the issue isn't so much as to where to find DEF, the issue is not trying to get screwed at the dealership buying 1/2 gallon Kruse bottles at $25+, when you can easily get one from an online retailer at $7.

So even with my upcoming trip, I will just carry the 1/2 gallon Kruse bottle with me as it's as compact as it can possibly be. And if prompted, I'll dump the 1/2 gallon in first, and see if message goes away, if not, I can either wait to get home or snip the crimps on the bottle and refill with bulk DEF, though I should have enough coverage to get home and do all this, after all I'm not leaving the trip at "999", so I have more than 1000 miles of coverage.

Also separately, I'm not going to invest in the Mercedes 10 liter + hose option. The hose alone is like $30 or so, plus there's a p/n change sometime around 2014 that made the hose non-adaptable to the new adblue bottle, so even more headaches to sort out. I'll just modify the kruse bottle and refill 0.5 gallons at a time.


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## FredoinSF (Nov 29, 2009)

You're seriously overthinking this DEF stuff Flying Ace. I've had the warning come up in Sac while driving from SF to Reno then drove back to SF with warning on. Worst part of it was vitriolic verbal communication from SO who was spazzing out about the no start potential. Refilled passive tank with 2.5 gallon jug when convenient and life was gay again. 
I always seem to get warning in Sac with SO in car, now I refill on whatever side of the hill I'm on to avoid negative energy from passenger side, not because of no start fear.

Sent from my iPad using Bimmerfest mobile app


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## Flying Ace (Jan 26, 2015)

Kk


FredoinSF said:


> You're seriously overthinking this DEF stuff Flying Ace. I've had the warning come up in Sac while driving from SF to Reno then drove back to SF with warning on. Worst part of it was vitriolic verbal communication from SO who was spazzing out about the no start potential. Refilled passive tank with 2.5 gallon jug when convenient and life was gay again.
> I always seem to get warning in Sac with SO in car, now I refill on whatever side of the hill I'm on to avoid negative energy from passenger side, not because of no start fear.
> 
> Sent from my iPad using Bimmerfest mobile app


Haha thanks, BMW should have an option where if SO is anal retentive about DEF refill, then remove 999 warning message, as you will hear it more often than you'll see it


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