So there is a market/problem with these tanks if people are offering repair service. The only problem with the one link is the fact you cannot purchase an outright exchange tank, so you must have the car down/apart while the tank is out unless the tank can easily be removed and the vehicle can still be driven.

One more problem system to live with!!!

It is a body shop and they have X5 with active tank that is broken from an accident. I want to take a look inside and take some pics.

Or go VW way :D
There is a transfer pump on the top of the active tank. The tank on the links is sold without the pump. Broken pump doesnt trigger CEL, but when there is DEF left for ~1000 miles the car will send you message-"No start in 995 miles" :stickpoke
We are exchanging some ideas for external sensor in another thread here. AT the end of the day the level sensor could be emulated too.

Don't forget to take a meter with you and measure the temp sensor resistance.:thumbup:

I would appreciate an explanation how the active and passive DEF tanks work. Which one gets filled when needed? Do either of them need to be drained prior to re-fill? Just curious.

Yea, aware of the other thread, I have commented on that too.

I wonder what would happen if a fixed resistance was inserted for the level sensor if this would trigger any other problems?

Is this like coolant or windshield washer fluid where you can physically see how full you fill the tank?

Active tank is small and heated when needed to prevent freezing. Passive tank is larger and passively heated by adjacent components. When the active tank level is low, DEF is transfer pumped from the passive tank to the active tank.

Neither needs to be drained prior to fill. That was an early BMW protocol, perhaps until it was realized how soluble urea is in water.

My intention is to not fill the active tank, to fill the passive tank only.

There is no way to see how full the active tank is. My guess is that it is a "fuel reserve" type of sensor that tells you when the fluid gets below a certain level.

And... mine failed (passive tank level sensor). When the tank is full I get no CEL. When the tank is low I get a CEL.

Member PIXLFIX over on Bimmerfest repaired their failed active tank level sensor by adding resistance between the two leads of the sensor. I will likely do the same if I can't find a cheap secondhand tank or sensor to swap in.

Can you post a link to the discussion?