35D Active DEF tank forensics

[bawareca]

So I finally got my hands on this broken active DEF tank for 2012 X535D. It is not a big deal to be opened, same as a gas tank screw-in cap on the top. It has 2 connectors with 8 wires altogether. 2 of them appear to be for a heater, 2 are for the temp sensor and 2 are for the level sensor and the other 2 probably for the urea quality sensor(someone please check the wiring diagrams). On the big connector 2 thick wires appear to be for the heater (you can see it on the bottom of the pot which goes inside the tank) and the other 2 are the temp sensor. The other 2 sensors are on the small connector.
I didnt have my thermometer with me, so I did a very rough measurments of the temp sensor resistance. So at around 65F it was 11k and went down to 7k when it was exposed on the sun for some time, roughly 85F.
I am sure a very simple emulator for the level and temp sensors could be made.
On to the pictures:

[Socale39]

I like where you are going with this.

[Ozer]

Yes!! Im hoping it wont be long till you come up with a solution for this issue
Keep up the great work!

[split71]

Does this unit have a good temp sensor? If so, it looks like a 10k NTC thermistor will work. I have one I can send to anyone that wants to test it.

Keep in mind, this is a 4" long probe a wouldn't be a direct replacement, but could work as an emulator.

Various resistance values of this sensor:
24k ohms @ 45F
14.75k @ 60F
11.72K @ 70F
8.4k @ 85F

[bawareca]

^^^ Looks like this will work.

[jfoj]

I'm just curious about all of this, I do not have a Diesel, however, I like to understand the whys and why not of things.

1. I assume this "cup" goes into a larger tank? This assembly is somewhat like a fuel pump/sender that drops in a fuel tank?

2. Is there not a pump as part of this assembly? How does the Urea get out of the tank?

3. Is this assembly available separately or do you have to purchase and replace the entire tank assembly? Seems to me this could be/should be a serviceable part.

4. I assume the heater is the vertically mounted cylinder? Not sure this is a wise set up because I assume at times this "well" may not always be full? Maybe a heater coil in the very bottom would have been a better idea.

5. What is causing the temperature sensors to fail? I assume possible corrosion/liquid intrusion? Temperature sensors are typically pretty robust unless the problem is not with the sensor and it is with the wiring/connectors.

6. The top appears to be broken, was this from accident damage or trying to open and remove the insert?

Anyway, it will be interesting to see what can be done to improved on this. If BMW does not come out with a serviceable part, especially if the insert can be removed much easier than the entire tank assembly, I could see a possible market with what appears to be a higher than expected level of failures.

[bawareca]

1. Correct.
2. No pump. I guess the fluid is scavenged and sucked from the tank by the exhaust.
3. The whole tank. The tank itself is probably the cheapest part, there is no reason for BMW to sell you what you see on the picture for 95% of the price of the whole assembly and risk a botched installation by inexperienced or careless mechanics.
4. Read my post. The heater is on the bottom of the cylinder.
5. Good question.
6. it was broken by car accident.
The overall design is not bad at all and it works fine when it works.

[jfoj]

Thanks for the response.

I guess what gets me is if the heater/temp sensor module/canister could be easily replaced, even if I had to buy the tank, I might be inclined to just swap the heater/temp sensor module/canister.

But I am not seeing $800 or what ever in all of this.

We all know that restive heaters and thermistors are very low in cost.

Maybe the rotational/flow molding of the strange side tank is expensive?

[ZetaTre]

There's no "urea quality sensor" -> the quality of the urea is assessed by changing the duty cycle of the metering unit and observing the shift in the post-SCR NOx sensor.
The 4 wires are all for the level sensor: there's a common, and 3 wires for the "FULL", "HALF" and "LOW" probes.

There is a pump, actually 2: there's a transfer pump and a supply module. The first one simply moves fluid from the passive to the active, the second one pressurizes the line going to the "metering unit" which is nothing more than in injector with some cooling fins.

Great work on this!!!!!

[ard]

Originally Posted by ZetaTre

There's no "urea quality sensor" -> the quality of the urea is assessed by changing the duty cycle of the metering unit and observing the shift in the post-SCR NOx sensor.!!!

Which (I think) is why a 'bad urea' warning can be due to a clogged DEF nozzle: the duty cycle goes to its maximum limit; the DDE does not see the NOX values respond as they should; it then declares 'must not be def in the tank'