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There is no VW substitute for the passive tank. Until the correct Bosch replacement ACTIVE tank became available, people were rigging a VW active tank to fit as a replacement. I can't imagine what could be wrong with your passive tank - it's just a storage tank with nothing really to go wrong. Edit... oh, now I see - the level sensor has failed. Has no one figured out a way to fix the level sensor without replacing the whole tank?

2nd Edit: Are you sure the passive tank level sensor is the culprit of your CE light? Frankly, I couldn't care less about that level sensor. Most diesel drivers have adopted the practice of filling their passive tanks with 2.5 gal. of DEF once they get the 1K mile countdown warning (which is triggered by the level in the active tank). I'm actually only putting in a gallon or so, as my 8-10K annual mileage means 2.5 gal. of DEF would sit out in the elements (sun) longer than I prefer.

AM.
 

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Did you mean "active" instead of "passive" in your comment. "Most diesel drivers have adopted the practice of filling their passive tanks with 2.5 gal"

The code that Carly and Indy pulled are: 4BCC (Passive Tank Level Sensor) and 4976 (NoX) so that's all I have.

I actually filled the Active Tank today and it barely took 500ml which means it was pretty full already. So there's no transfer from Passive to Active anyway.

Should I just drain out the passive tank and keep it empty? I'm going to take the car on a long drive for 250 miles and see if active tank is even being used - hopefully it's not the metering valve but again Indy said - he only pulled the above 2 codes.
No, I wrote exactly what I meant. Why do you say your transfer from passive to active is not working? The fact your active tank was nearly full is an indication the transfer system is working as designed. Emptying your passive tank is not going to fix anything. You have a level sensor issue, which is a non-critical sensor. I suspect (but am not sure) that sensor issue will not cause a CE light. I'd worry more about your NOX sensor issue. I suspect once you've remedied that, your CE light will go off. Regardless, your NOX sensor is still the more urgent issue.

I was thinking the following potential solutions just not sure in what order:

Xemodex Passive Tank Repair (Just like you I'm not sure if it's the passive Tank at all)
Change upstream Nox Sensor
Clean EGR Valve
(Clean DEF Injector + Change Metering Valve) - That's what someone did in of the threads.

As I said, I'd fix the NOX sensor issue (don't automatically assume you need a new one - firing the parts canon at a BMW is expensive). Forget all the other stuff until you solve your NOX code. Then it's up to you if it's worth $700+ to fix the level sensor in the passive tank (wouldn't be to me).

Edit: I did a little more digging on this. The passive tank level sensor WILL set a CE light and it may prevent the transfer pump from running (didn't entirely verify). There is a somewhat easy "fix" that may make more sense than spending $700+: 35d 4BCC- Reducing Agent Passive Tank Sensor Failure

Essentially, you'll install a resistor to "trick" your car into believing the tank is full which will allow the transfer function to operate as designed. The downside is that you'll need to ensure you don't let the passive tank go empty, as that could lead to transfer pump damage. Personally, I'd rather have that minor adjustment than to spend the money replacing the tank or having the sensors fixed. YMMV.

AM.

AM.
 
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