35d 4BCC- Reducing Agent Passive Tank Sensor Failure - Page 3 - Bimmerfest - BMW Forums



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X5 E70 (2007 - 2013)
E70 BMW X5 produced between 2007 and 2013. Discuss the E70 X5 with other BMW owners here.

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  #51  
Old 10-30-2019, 10:37 AM
jesus_man jesus_man is offline
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I am trying to "fix" this myself with a resistor. I am adding a resistor between the blue and black wires that I believe lead to the top of the tank and is for the level sensor for the passive tank. (my code is the 004bcc). I get a 10k OHM resistance before applying my fix. When I add the resistor inline, I get 5k ohm. I have cleared the code with Carly and waiting for it to return.

Anyone ohm these blue and black wires just to verify? What should a good sensor ohm at? I'm just not sure this will fix my issue when I was getting a 10k ohm reading prior to the fix. If it matters, my resistors are 10kohm, 1.8watt



If you are doing this yourself, I found it easiest to pop the signal magnifier off the side of the tank (slide catch on the bottom one way or the other and push box upward). Then you can better see how the connector pictured below comes off it.

Thanks for any help! Want this CEL gone and am not willing to pay the dealer $2500.
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  #52  
Old 10-31-2019, 12:27 PM
Nonsuch Nonsuch is offline
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Quote:
Originally Posted by jesus_man View Post
...I get a 10k OHM resistance before applying my fix. When I add the resistor inline, I get 5k ohm...
The sensor you tried to "fix" was likely fine.

There are 2 sensors, full and empty. When immersed in DEF the sensor will be low resistance (a short). When not immersed the sensor should be 10k ohm.

You might want to check the resistance across the other 2 wires. If it reads "open" then install a 10k ohm resistor across those wires.
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  #53  
Old 10-31-2019, 12:36 PM
jesus_man jesus_man is offline
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Will try that! Thank you!!I didn't realize there are two level sensors in the tank.
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  #54  
Old 11-04-2019, 08:37 PM
jesus_man jesus_man is offline
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Quote:
Originally Posted by Nonsuch View Post
The sensor you tried to "fix" was likely fine.

There are 2 sensors, full and empty. When immersed in DEF the sensor will be low resistance (a short). When not immersed the sensor should be 10k ohm.

You might want to check the resistance across the other 2 wires. If it reads "open" then install a 10k ohm resistor across those wires.
You nailed it my friend, or at least I have had no check engine light for 500 miles!! I will post some pictures soon of how I did it with no permanent mods to any parts. Then put the panel back in place and wait for the other shoe to drop.
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  #55  
Old 11-04-2019, 09:32 PM
Nonsuch Nonsuch is offline
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Quote:
Originally Posted by jesus_man View Post
You nailed it my friend, or at least I have had no check engine light for 500 miles!!...
I have had no check engine light for 25,000 miles
(at least none related to the Passive Tank or 4BCC code)
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  #56  
Old 11-05-2019, 06:24 PM
jesus_man jesus_man is offline
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Here is how I did mine, somewhat of a step-by-step
1. Pull this panel off the bottom paying careful attention to how it overlaps or underlaps adjacent panels.


As mentioned, you will find passive tank under the drivers seat and to the left of the DPF. On the vertical surface of the rear of the tank, you will find the signal amplifier. Using a screwdriver, push catch to the side and push the amp upwards:


This gives you better access to both of the sensors wiring.

The catch to disconnect the sensors from the amp is where my screwdrive is. Gently pry that up and pull the gray plastic part out:


Press the gray plastic down to release the connector from the amp revealing the wires from each sensor. Black & Blue for the upper sensor and orange (red?) and yellow for the lower sensor. Ohm each pairs of wires to see which sensor has failed. My failed sensor was reading very sporadically.

I did not want to permanently modify the wiring (although it's a $60 harness) so I wanted to try something different. While testing, I broke a small cover off the male end of this connector, but that gave me an idea.
Bending the ends of the resistor wires like a fish hook, and coating them in dialectic grease, I stuffed the ends up into the faulty bays for the wires of the faulty harness and retested the ohms. After a successful reading, I stuffed the rest of the wire and the resister up into the connector.


Plugged it back in, cleared the codes using Carly and haven't had a problem for 500+ miles. Time will tell is my mod will hold, but so far I am pleased.

How many miles do you usually go before topping off the DEF because obviously the transfer pump will run since it believes the passive tank is always full?
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