Fixed my 4BCC CEL
 

Hey guys, new owner/member here. Picked up a 2011 X5D and it had a CEL pop up for 4BCC on the drive home. It was a deal and we knew it was going to have issues. Dig into the forums here (and bimmerpost) to research best practices for repair/upgrades to issues.

Found the price of the passive def tank ridiculous so I went and built myself a, let’s just say highly functional, 4 wire patch harness out of a trailer wire extension because the connector is basically water tight and the wire colors basically match the existing level sensor harness. 10k ohm resistor soldered in between each wire and the signal wire. With a second harness cut in two and wired in I can replace or update the harness if needed.

So I crawled under the car, pulled the passive tank out and went wait. Where is the 4 wire harness? Time out, back to forum, realize I built a harness for the active tank. Doh! Go back out, measure resistance on each level sensor and find the top sensor has an open circuit.

Started looking at where the best place to wire a resistor would be, and I looked at the end of the harness.

Well, I think a resistor will fit in that corner and I can just stick some leads into the connectors.

Well what do you know, it works. Plugged everything back in and cleared the code. Two days later and still clear. Going to fill the tank and get our smog test done.

Happy to help with any questions and will do a proper intro post once I’m on a computer and not my phone. Sorry the photos wouldn't load directly from google photos, so I had to shrink them and attach manually.

Hello, if you don’t mind, can you explain a bit in detail what you did? I am getting the 4bcc error code too. There are two sensors I’m thinking on the passive tank. One for high level and one for low level def.. As a I have DEF in the tank what should the resistance reading be on the wiring? Is it a 10k ohms resistance when the tank is empty or full or doesn’t matter on fill level?

On the 335d i was able to buy the active/passive tank “basket type” sensors from VW rather than purchasing the entire DEF tank from bmw. That was a direct diy install.

Thanks

My issue was with the upper sensor. Take a multimeter and measure the resistance between both terminals of the sensor. If it's open (infinite resistance) then just slap the 10k ohm resistor in the connector and reconnect. Same should work for the lower sensor too.

adriang, would you mind sharing the VW part numbers for the sensors mentioned above. Also, if you have any pictures I would really appreciate you posing it.


Thank you!

ttt

watching this one closely

in 2017 it was around $330CAD+tax from the VW dealership. The VW part # is 7L6 198 970 A

I have a step by step instructional with pictures on the internet if you search adriang active tank sensor replacement

Can you please specify what 10k resistor your used? 1 watt?1%? Also, was this for the temp sensor or level sensor? Thanks

I just used a 10k ohm 3 watt I believe. A 1 watt would be fine as it is just a resistor to complete the circuit when the level sensor reads low. There is no heater in the reserve tank.

Excellent, thanks.

looking at the picture, looks like a sub one watt


the dimensions will tell you...1/4 is 6.5mm long by 2.5mm...1/2 is 8.5mm L x 3.2 dia

Just got this issue and a $3508 quote from the stealership so... 10k Ohm resistor it is.

One question: do you have to pull the actual tank in order to do this? Or can everything be done with the tank installed? Would like to avoid pulling the exhaust and whatnot if I can.

@bobman21 - Did you do this fix already? Can you share some wisdom?

Yeah, ended up being pretty straightforward, although I'm struggling to remember the details now 30 months later. I've been trouble-free since the fix FTR. Roughly:

1. Underbody panels come off. Tank is located on the driver's side roughly under the driver's seat, maybe a bit farther back where the passenger's feet go.
2. IIRC it has a drain plug. I drained the liquid to save myself on the mess and the weight of unbolting it and pulling it down.
3. The exhaust does not need to come off for this job. It's pretty obvious what you need to do when you get the underbody panels off, although I remember it being mildly annoying (everything went back together without any hassle or needing to mark screws/parts or anything like that).
4. This part I don't remember clearly: how many sensors there are and whether you have to test each one or if it's always the same one that's bad to cause the code. Anyway, there are 2-3 sensors. One at the top of the tank (hence having to remove it to test), one at the bottom, and (maybe) one in the middle. IIRC you take your multimeter and measure the resistance. I think you drain the liquid also so that you can check whether each sensor is offering the right resistance. 10k Ohms is what you want to see. If you don't see 10k Ohms (I believe you just have an open circuit otherwise) then you know the sensor is bad. Again, you'll need to corroborate this with other posts/threads of exactly how to test, this is just a summary of what my (reasonably lazy and inexperienced) approach was and the results.
5. Whichever sensor is bad is the one you bridge. To avoid having a dangling sensor/water intrusion, I took a 10k Ohm resistor and stuffed it into the connector, bridging the two leads of the connector (to be clear: the connector side, not the sensor side. It fits together better that way). This is a tight fit back together because it's not supposed to have a resistor in there... but with enough coaxing it goes back together.
6. Put everything back into its home.

You may be wondering where you get a 10k Ohm resistor. It's not like you can go to a Radio Shack anymore. I happened to have a breadboard kit I bought on Amazon for <$20. But I'm sure you could just buy an assortment of resistors for even cheaper. These are the little guys... the resistor itself is probably 1-2 mm in diameter, and 4-5 mm long. The leads are thin. I just typed "resistor" into Amazon... any of those first hits are fine.

Keep in mind the ECU will now always think the tank is full... so you'll need to be proactive about remembering to fill.

Thx a lot Bobman. This really helps me to take up on this job and save 3500.00. Xemodex is also $900 and I'm guessing they do the same.

My main question/clarification is "where to insert the resistor" and in which pins. I saw many threads and it's hard for me to figure out if:

1.) Do I need to use 1 resistor OR 2 resistors?

2.) Does the resistor go from pin1 to pin2?

Adding some pics so you can guide me better; thx a lot!!

Well that's a pickle... I have no memory of there being 4 pins instead of 2. I suppose if I found myself in your situation right now, I would unplug the other sensors and look for which specific combination of pins (on a working sensor) gives me 10k Ohm. Then just bridge those two pins on the connector for the faulty one.

To answer your question more directly: 1) you only do one bridge (one resistor). 2) Per above, I don't remember. However, in that second photo it does look like it's Pin 1 and Pin 2. The placement of the resistor is just to accommodate routing for the connector to go back. There's no fancy business happening off screen in those folds. I don't think I put my connector back together like that... I think there's multiple ways for the resistor to fit. But it really is just a simple bridge of the two pins. My only question is that it doesn't look like the lead actually hits Pin 1 in that photo. Maybe it's just optics. That's the only reason I think you're safer to test a good sensor to make sure it's the right pins.

Re-reading post #1, there are two different tanks, two different sensor fixes...one is a two wire harness, the other is a 4 wire.



Maybe that helps a bit?

Are you talking about the active tank in the engine bay vs. the passive tank towards the rear? If so, I could be mistaken but I believe this specific code is for the SCR tank in the back.

yes 4BCC is for SCR / Passive Tank (10K Ohm resistor fix)

For Active tank - there's a cheaper VW part that can be used.

Thanks. Recently encountered 4BCC CEL, will reference this guide as a fix.

To avoid dropping the PASSIVE tank, could one simply cut the tank side harness and one splice in two resistor between the two wire pairs shrink wrap and call it a day?

What am I missing? Thank u

More details on passive tank location and sensor connectors
 

“Pull the passive tank” they said, “it will be easy” they said.

I wanted to add more details to what was posted in this thread. Not that it was extremely challenging, but it was time consuming. A couple of hours at least. I wish I was more organized, and created a real guide, but …

1. Remove all the panels under the car on the driver side that live between front and back wheels. You can see part of the tank when you take off one key panel, but it’s best to have them off to avoid breaking expensive and aging pieces of plastic and foam.
2. The tank is immediately forward of the gas tank on the driver side. It is enclosed in two polystyrene foam insulation shells.
3. There is a big black metal brace, with two nuts (13mm). Once removed, the tank will hang on hoses and wires, so figure out how to support it.
4. There are two more 13mm nuts side by side on the side bracket that’s stuck to the tank. It doesn’t slide off the tank, you need to remove the nuts from the car body.
5. Once you can see the big, silver sleeved hose, you will want to pull it off the tank, and drain it or plug it really well. This one has a worm clamp (6mm or 1/4").
6. There are two other hoses that need to be removed. The small one on the bottom has a permanent clamp you’ll have to break and replace later. Top thin hose has a gray button you press before pulling it off.
7. To make things difficult, various wires and hoses are stuck to the tank or brackets holding the tank. Two silver, 90 degree angled brackets can be removed EASILY by turning the metal piece 45 degrees. If you yank and pull, you’ll break off the plastic! Another wire can be removed by squeezing the top of the clip, and sliding it through.
8. There is a small hose in a C shaped clamp stuck to the side plastic corner bracket coming off the tank. Pop it off.
9. You will need to bend or remove part of the heat shield around the exhaust as you remove the tank
10. Once you unhooked everything, slide the bottom clamshell out and set it aside.
11. Pull out the tank, if it’s not moving, some wire or hose is snagged or needs to be disconnected.
12. The top insulating clamshell will stay in the car, as it has a hose that goes up somewhere.

The reason I took it off was to locate a leak and plug it up. But, I didn’t see any leak. I was told by forums that plastic leaks around the sensor and it gets on the wires and that’s why the sensors read wrong. But, my tank looks pretty clean. However, both sensors show 14-18 MEGA Ohms resistance (with and without fluid contacting them). I assume that is “open circuit”. Not sure. But I do get the 4BCC code. I will shove 10k resistors into both circuits. Both sensors have FO1C470061 and 13.06.2012-638-A markings on them.

As the post above pointed out, you don’t need to remove the tanks, you can simply access the harness after removing plastic panels. There was some confusion, but I think I can resolve it with the attached picture. There is a harness that is dedicated to the top and bottom level sensors, it is BOSCH 0280620694. It has a 4 pin connector (you see in other posts) going towards the ECU (black, blue, yellow, brown). Brown and yellow are on a short lead of the Y split, and black and blue are on the long lead. Brown and yellow connect to the bottom sensor, and black and blue connect to the top sensor. You can easily access the two pin connector on the bottom, but the two pin connector on the top requires removing the tank.

The 4 pin connector is plugged into a plug stuck to the metal cross brace. It has a little gray tab you can’t see from the bottom of the car, but you have to slide it out (away from the connection) before attempting to pull it off. That is where you can check impedance and shove resistors if you don’t want to remove the tank.

Hope this helps, feel free to ask questions.

Another version of resistor fix
 

I was a little unclear on previous posts, so I wanted to be more thorough in describing the fix.

1. Get a 1/8 W (125mW) 10Kohm resistor. See pictures with measurements. I got the cheapest one from eBay. Most likely, all 1/8W resistors will be about the same size.

2. I used the 4 pin connector for my insertion point. See above post: this is accessible without removing the passive tank. It is where the top sensor and the bottom sensor merge and plug into what looks like a CAN bus transmitter.

3. As you can see, I didn't have to Dremel anything. Resistors, lay flush in the slots that happen to be in the connector plastic already. It just plugged together smooth, but tight. Likely, you'll need to cut off ~1/4 inch of the resistor pins, my final length was 42mm, down from 60mm. Make sure to pre-form the resistor pins slightly as shown.

I reset the codes (make sure to have your car 12V charging, as to not blow up your FRM, like I did). The CEL didn't come back after a few long trips. Not really sure about the passive tank level detection, I didn't refill it after draining. Maybe now ECU permanently assumes tank is 1/2 full (unless it's a pessimist ECU). The resistance range for these sensors is 8K to 12K Ohms.