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Discussion Starter · #1 · (Edited)
Hi All,

I've been driving with the 4976 and 4BCC code for almost a year now (I got the CEL 1 month after 10 years had passed and I was at 80K but BMW NA said NO to goodwill after multiple tries). I got the codes via Carly before taking it to the Indy yesterday.

4976 - NoX Sensor
4BCC - Passive Tank

Anyway - I need to tackle the job now so went to the Indy who ran diagnostics and confirmed the above codes (see attachment) and the recommendation is to change the Passive Tank and NoX sensor = Total Quote $3400.00 which is a No Go ($2100 just for the passive tank, rest NoX and Labor)

After reading multiple threads etc - I'd go with the cheap VW part and that's where I need help to confirm the part number since there seem to be different revisions as well so I want to make sure I get the right one.

So far, I see that there are two part numbers: 7L6-198-970-A and 7L6-198-970

From one of the threads someone shared the below link but part numbers are 7L6-198-970-B and 7L6-198-970
https://www.ecstuning.com/b-genuine-volkswagen-audi-parts/rep-kit/7l6198970b/ but the ECS fitment says it doesn't work for E70 35d.

I also saw some threads mentioning at "Bosch" part but I can't find the part number. Can y'all confirm the correct part. Also, I'm in Houston so if there's an Indy you know who has done this before, do let me know.
 

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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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Discussion Starter · #3 · (Edited)
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.
Thx for the reply @Attacking Mid . 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.

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.

 

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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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On the note of the passive tank, might I suggest used from eBay, just swapped both the active and passive pumps on my 2013 X5 35i about 2 months ago and found both on eBay for less than $150... Work perfectly.
 

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Thx @Attacking Mid

Need to find out if I can change the NOX sensor myself. There are 2 and each costs 500+.

Forum members- Has anyone here changed the NOX sensor DIY? How easy difficult it is?
NOx sensors have to be calibrated. Also, be ready for some more bad news. NOx sensors are like O2 sensors, they have to agree. Best approach is both sensors to be replaced. But, wait, there is more: your SCR cat might be culprit or DEF injector. If they don’t do their job properly, it might show as bad NOx sensor.

Passive tank level sensor? Just put resistor and make sure you always have DEF.


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Discussion Starter · #8 ·
Thx for the reply Edycol. I need to plan the exact approach before I go to the dealership. The car is 11 yrs old with 87K and worth 9K. So, I want to have a plan and be smart about the sequence of "throwing parts at my expense". The CEL has been ON for a year :)

I had Indy to the diagnostics and they said replace passive tank and O2 sensor and that didn't make sense based on what I saw in Carly so will take it to the BMW dealership next week.

Should I have the DEF injector cleaned and Metering Valve changed + clear EGR valve even before going to BMW?

And then work on
1.) Nox sensors
2.) SCR Cat
3.) Passive Tank



NOx sensors have to be calibrated. Also, be ready for some more bad news. NOx sensors are like O2 sensors, they have to agree. Best approach is both sensors to be replaced. But, wait, there is more: your SCR cat might be culprit or DEF injector. If they don’t do their job properly, it might show as bad NOx sensor.

Passive tank level sensor? Just put resistor and make sure you always have DEF.


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Well, if you can clean it, it would not hurt I guess. My SCR cat died right around that mileage. BMW thought sensors were an issue, but it turned out to be SCR cat.


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Discussion Starter · #10 ·

Is this the thread you're talking about?

I'll take it to BMW sometime soon but really thinking is 4-5K (SCR Cat/NOX sensors) worth spending on a 9K car :)

Well, if you can clean it, it would not hurt I guess. My SCR cat died right around that mileage. BMW thought sensors were an issue, but it turned out to be SCR cat.


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